Positively chargeable toner

Abstract

This positively chargeable toner has sufficient positive chargeability while containing strontium titanate particles as an external additive, has excellent solid followability, and is less susceptible to fogging and toner ejection under a high-temperature and high-humidity environment. The positively chargeable toner contains colored resin particles and an external additive containing strontium titanate particles. The strontium titanate particles are each doped with a metal element other than titanium or strontium, and at least a part of the particle surface of the strontium titanate particle is coated with a fatty acid alkali metal salt.

Description

Positively charged toner

[0001] This disclosure relates to a positively charged toner used for developing electrostatic latent images in electrophotography, electrostatic recording, and electrostatic printing, etc.

[0002] In image forming apparatuses such as electrophotographic devices, electrostatic recording devices, and electrostatic printing devices, an image forming method is widely implemented in which an electrostatic latent image formed on a photoreceptor is developed with an electrostatic image developing toner (sometimes simply referred to as "toner" in this disclosure) to form a desired image, and this method is applied to copiers, printers, facsimile machines, and their multifunction devices. In order to improve the functions of the toner, such as its charge stability and fluidity, and to obtain the desired printing performance, external additives such as inorganic fine particles or organic fine particles are usually added to the surface of the toner. On the other hand, if the amount of external additive added is increased in order to obtain the desired characteristics, the filming phenomenon is more likely to occur. In response to this, Patent Document 1 proposes using strontium titanate as an external additive.

[0003] Furthermore, Patent Document 2 states that in negatively charged toner, using strontium titanate as an external additive can suppress excessive charging.

[0004] Japanese Patent Publication No. 10-10770 Japanese Patent Publication No. 2019-184793

[0005] However, it was difficult to improve the performance of positively charged toner by using strontium titanate as an external additive.

[0006] The objective of this disclosure is to provide a positively charged toner that contains strontium titanate particles as an external additive, has sufficient positive charge properties, excellent conformability to solid areas, and is less prone to fogging and toner ejection in high-temperature and high-humidity environments.

[0007] In other words, the present disclosure provides the following positively charged toner: [1] A positively charged toner comprising colored resin particles and an external additive containing strontium titanate particles, wherein the strontium titanate particles are strontium titanate particles doped with metal elements other than titanium and strontium, and at least a portion of the particle surface is coated with an alkali metal fatty acid salt.

[0008] [2] The positively charged toner according to [1], wherein the colored resin particles contain a quaternary ammonium salt-containing copolymer as a positively charged charge control agent. [3] The positively charged toner according to [1] or [2], wherein the metal element doped into the strontium titanate particles is lanthanum. [4] The positively charged toner according to any one of [1] to [3], wherein the coating amount of the fatty acid alkali metal salt is 4% by mass or more and 20% by mass or less with respect to 100% by mass of the strontium titanate particles. [5] The positively charged toner according to any one of [1] to [4], wherein the external additive further comprises an external additive different from the strontium titanate particles. [6] The positively charged toner according to any one of [1] to [5], wherein the external additive further comprises silica particles, and the ratio of the silica particle content to the strontium titanate particle content is 0.5 to 10.0.

[0009] According to this disclosure, it is possible to provide a positively charged toner that contains strontium titanate particles as an external additive, has sufficient positive charge properties, excellent conformability to solid areas, and is less prone to fogging and toner ejection in high-temperature and high-humidity environments.

[0010] In this disclosure, the "~" in numerical ranges means that the numbers before and after it are included as the lower and upper limits, respectively. Furthermore, among the numerical values ​​described in this disclosure that may include decimal places, unless otherwise specified, the numerical values ​​are obtained by rounding the digit that was one place smaller than the smallest digit included in the numerical value. Furthermore, in this disclosure, (meth)acrylate refers to acrylate and methacrylate respectively, and (meth)acrylic refers to acrylic and methacrylic respectively.

[0011] 1. Positively Charged Toner The positively charged toner of this disclosure contains colored resin particles and an external additive containing strontium titanate particles, wherein the strontium titanate particles are doped with metal elements other than titanium and strontium, and at least a portion of the particle surface is coated with an alkali metal fatty acid salt.

[0012] Because strontium titanate is positively charged, using strontium titanate particles as an external additive in positively charged toner is expected to improve charge build-up and increase the amount of charge, thereby suppressing toner ejection. However, the Discloser has found that even when strontium titanate particles are used as an external additive in positively charged toner, it is difficult to suppress toner ejection in high-temperature and high-humidity environments. Furthermore, the use of strontium titanate particles tends to cause problems such as deterioration of solid color tracking and fogging in high-temperature and high-humidity environments. These problems are presumed to be due to insufficient toner fluidity and charge stability caused by the strontium titanate particles, and also because the positive charge imparting effect of the strontium titanate particles is insufficient. In contrast, the positively charged toner of this disclosure uses strontium titanate particles that are doped with titanium and metal elements other than strontium, and at least a portion of the particle surface is coated with a fatty acid alkali metal salt. As a result, it has sufficient positive charge, excellent solid-coverage tracking, and is less prone to fogging and toner ejection in high-temperature and high-humidity environments. The reason for this is unknown, but it is presumed to be as follows: Strontium titanate particles usually have a perovskite crystal structure, making them cubic or rectangular and having corners. Due to the shape of such strontium titanate particles, the toner tends to have insufficient fluidity, and the concentration of charge at the corners of the strontium titanate particles can easily lead to problems with charging characteristics, such as poor toner charging startup. In contrast, the strontium titanate particles used in the positively charged toner of this disclosure are doped with titanium and metal elements other than strontium, resulting in a chamfered and rounded particle shape. As a result, the strontium titanate particles used in this disclosure do not degrade the charge rise of the toner, have good dispersibility and fluidity, and can exist in a well-dispersed state on the surface of the toner particles, thereby imparting fluidity and positive charge properties to the toner. Furthermore, at least a portion of the surface of the strontium titanate particles used in this disclosure is coated with a fatty acid alkali metal salt.Alkali metal fatty acid salts enhance the positive charge properties of strontium titanate particles while also imparting hydrophobicity to them. Strontium titanate particles surface-treated with such alkali metal fatty acid salts exhibit superior fluidity-enhancing and positive charge-enhancing effects on toner, improving the toner's charge rise and charge stability. Therefore, the strontium titanate particles contained as an external additive in the positively charged toner of this disclosure are excellent in improving the toner's fluidity and positive charge properties, and thus improve the toner's charge rise and charge stability. As a result, the positively charged toner of this disclosure has sufficient positive charge properties, excellent solid-coverage tracking, and is less prone to fogging and toner ejection in high-temperature and high-humidity environments.

[0013] The positively charged toner of this disclosure may be used as a one-component toner (developer), or it may be mixed and stirred with carrier particles to be used as a two-component developer. However, it is preferable to use it as a one-component toner (developer) because the effects of the strontium titanate particles described above are easily exhibited.

[0014] The following describes, in order, the external additives contained in the positively charged toner of this disclosure, the colored resin particles and their manufacturing method, and the physical properties of the positively charged toner of this disclosure.

[0015] 1-1. External Additives The positively charged toner of this disclosure contains at least strontium titanate particles as an external additive, and may optionally contain other external additives.

[0016] The strontium titanate particles contained in the positively charged toner of this disclosure are doped with titanium and metal elements other than strontium (hereinafter sometimes referred to as "dopants"). As a result, the strontium titanate particles have a rounded shape, which improves their dispersibility and fluidity.

[0017] The dopant for strontium titanate particles can be any metallic element other than titanium and strontium, and is not particularly limited. However, at least one selected from the group consisting of La, Mg, Ca, Sn, and Si is preferably used because it is easy to dope and allows for easy control of the shape of the strontium titanate particles, with La (lanthanum) being particularly preferred.

[0018] The amount of dopant in strontium titanate particles is not particularly limited, but in order to improve the dispersibility and fluidity of the strontium titanate particles, the amount of dopant per 100 mol% of strontium may be, for example, 2 mol% to 15 mol%, 4 mol% to 15 mol%, or 6 mol% to 12 mol%. The type of dopant contained in the strontium titanate particles can be confirmed by X-ray fluorescence analysis (XRF), and the amount of dopant can be measured by the X-ray fluorescence fundamental parameter method (FP method) in accordance with JIS K 0119:2008.

[0019] Furthermore, the strontium titanate particles contained in the positively charged toner of this disclosure have at least a portion of their surface coated with an alkali metal fatty acid salt. As a result, the resulting positively charged toner has good positive charge properties, hydrophobicity and fluidity, suppresses fluctuations in charge and aggregation, and exhibits excellent dispersibility. In this disclosure, "at least a portion of the particle surface coated with an alkali metal fatty acid salt" means that the particles are surface-treated with an alkali metal fatty acid salt by a general method. In other words, the strontium titanate particles used in this disclosure are strontium titanate particles surface-treated with an alkali metal fatty acid salt.

[0020] In the strontium titanate particles used in this disclosure, the amount of fatty acid alkali metal salt coating per 100% by mass of the strontium titanate particles is not particularly limited, but may be, for example, 4% by mass or more and 20% by mass or 5% by mass or more and 15% by mass. If the amount of fatty acid alkali metal salt coating is above the lower limit, the charging characteristics of the strontium titanate particles, and consequently the charging characteristics of the toner, can be improved, thereby further improving the effect of improving the toner's ability to follow solid areas and suppressing the occurrence of fogging and toner ejection in high-temperature and high-humidity environments. On the other hand, if the amount of fatty acid alkali metal salt coating is below the upper limit, the release of fatty acid alkali metal salt from the strontium titanate particles can be suppressed, making it easier to control external additives. In the above-mentioned amount of fatty acid alkali metal salt coating, 100% by mass of strontium titanate particles means that the mass of the strontium titanate particles after surface treatment is 100% by mass. The amount of alkali metal fatty acid salt coating per 100% by mass of strontium titanate particles can be calculated from the amount of alkali metal fatty acid salt applied, the adhesion rate of the alkali metal fatty acid salt, and the mass of the strontium titanate particles obtained after surface treatment. Here, the adhesion rate is a value expressed as a percentage obtained by analyzing the carbon content of the sample using a carbon-sulfur analyzer and dividing the measured value by the carbon content when the theoretical amount of surface treatment agent is adhered.

[0021] In the fatty acid alkali metal salt used in the above strontium titanate particles, the fatty acid moiety (R-COO － The fatty acid (R-COOH) that induces ) is not particularly limited, but is preferably a fatty acid having a chain structure, more preferably a saturated fatty acid having a chain structure, and even more preferably a straight-chain saturated fatty acid, from the viewpoint that it is excellent in improving the toner's ability to follow the toner's surface and in suppressing the occurrence of fogging and toner ejection in high-temperature and high-humidity environments. Furthermore, the number of carbon atoms in the alkyl group of the saturated fatty acid is not particularly limited, but from the same viewpoint as above, is preferably 12 to 24, more preferably 14 to 22, and even more preferably 16 to 20.

[0022] There are no particular limitations on the fatty acid used as a raw material for the fatty acid alkali metal salt, and examples include lauric acid (CH ３ (CH ２ ) １０ COOH), tridecanoic acid (CH ３ (CH ２ ) １１ COOH), myristic acid (CH ３ (CH ２ ) １２ COOH), pentadecanoic acid (CH ３ (CH ２ ) １３ COOH), palmitic acid (CH ３ (CH ２ ) １４ COOH), heptadecanoic acid (CH ３ (CH ２ ) １５ COOH), stearic acid (CH ３ (CH ２ ) １６ COOH), arachidic acid (CH ３ (CH ２ ) １８ COOH), behenic acid (CH ３ (CH ２ ) ２０ COOH), lignoceric acid (CH ３ (CH ２ ) ２２ COOH), and the like. Among these, palmitic acid, heptadecanoic acid, stearic acid, arachidic acid and behenic acid are preferred, and stearic acid is particularly preferred, because these fatty acids are excellent in the effect of improving solid area followability of toner and the effect of suppressing occurrence of fogging and toner scattering in a high-temperature and high-humidity environment.

[0023] In the alkali metal fatty acid salt used in the above-mentioned strontium titanate particles, the alkali metal is not particularly limited, but at least one selected from the group consisting of Li, Na, K, Rb, and Cs is preferred, with Na being particularly preferred, due to its excellent effect in improving the toner's ability to follow the toner's surface and suppressing fogging and toner ejection in high-temperature, high-humidity environments. The alkali metal fatty acid salt can be used alone or in a mixture of two or more types.

[0024] The number-average primary particle size of the strontium titanate particles is not particularly limited, but it may be, for example, 10 to 100 nm, 20 to 60 nm, or 30 to 40 nm, as it is excellent in improving the toner's ability to follow solid areas and in suppressing fogging and toner ejection in high-temperature and high-humidity environments.

[0025] In the positively charged toner of this disclosure, the content of the strontium titanate particles is not particularly limited, but may be, for example, 0.2 parts by mass or more and 2.0 parts by mass or 0.5 parts by mass or 1.5 parts by mass or 0.8 parts by mass or more and 1.2 parts by mass or less per 100 parts by mass of colored resin particles. When the content of the strontium titanate particles is above the lower limit, the effect of improving the charge rise of the toner is high, while when it is below the upper limit, the effect of improving the fluidity and fixation of the toner is high. Furthermore, when the content of the strontium titanate particles is within the above range, the effect of improving the solid followability of the toner and the effect of suppressing fogging and toner ejection in high temperature and high humidity environments can be further improved. The strontium titanate particles can be used individually or in a mixture of two or more types.

[0026] The positively charged toner of this disclosure preferably further contains an external additive different from the strontium titanate particles described above. The external additive different from the strontium titanate particles can be selected from those conventionally used as external additives for toners, and is not particularly limited. Examples include inorganic fine particles such as silica, titanium dioxide, aluminum oxide, zinc oxide, tin oxide, calcium carbonate, calcium phosphate, and cerium oxide; organic fine particles such as polymethyl methacrylate resin, silicone resin, and melamine resin; and metal soap fine particles such as zinc stearate and magnesium stearate. The positively charged toner of this disclosure preferably further contains inorganic fine particles different from the strontium titanate particles as an external additive, in order to improve the toner's fluidity.

[0027] The inorganic fine particles are preferably subjected to hydrophobic treatment. Examples of hydrophobic agents used to hydrophobicize the inorganic fine particles include silane coupling agents, silicone oils, fatty acids, and fatty acid metal salts. Among these, silane coupling agents and silicone oils are preferred. Furthermore, amine-based hydrophobic agents are preferred as they improve the charging characteristics of the positively charged toner. Examples of amine-based hydrophobic treatment agents include aminosilane compounds such as γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, aminosilane, N-(2-aminoethyl)3-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane; amino-modified silicone oils such as dimethyl(aminoethylaminopropyl)methylsiloxane, dimethyl(aminoethylaminopropyl)ethylsiloxane, diaminopropyltetramethyldisiloxane, and dimethyl(aminoethylaminopropyl)methylcyclosiloxane; and the like.

[0028] The inorganic fine particles included as an external additive along with the strontium titanate particles are not particularly limited, but from the viewpoint of improving the fluidity of the toner, at least one selected from the group consisting of silica particles, titanium oxide particles, and aluminum oxide particles is preferred, at least one selected from the group consisting of silica particles and aluminum oxide particles is more preferred, and silica particles are particularly preferred.

[0029] When the positively charged toner of this disclosure contains silica particles as an external additive, the ratio of the silica particle content to the strontium titanate particle content (silica particles / strontium titanate particles) is not particularly limited, but may be, for example, 0.5 to 10.0, 0.6 to 9.0, or 1.0 to 2.0. When the above ratio is within the above range, the effect of improving the fluidity of the toner can be further enhanced.

[0030] The number-average primary particle size of the above-mentioned silica particles is not particularly limited, but from the viewpoint of ensuring proper toner fluidity, it may be, for example, 5 to 300 nm, 6 to 200 nm, or 7 to 100 nm.

[0031] The positively charged toner of this disclosure may contain multiple types of silica particles with different number-average primary particle sizes as an external additive. For example, it is preferable to contain two or more types selected from the group consisting of silica particles A with a number-average primary particle size of 36 to 100 nm, silica particles B with a number-average primary particle size of 15 to 35 nm, and silica particles C with a number-average primary particle size of 6 to 14 nm, and it is more preferable to contain silica particles A, B, and C. Including multiple types of silica particles with different particle sizes as an external additive tends to improve the fluidity of the toner.

[0032] The number-average primary particle size of silica particle A may be 40 to 80 nm or 45 to 70 nm, from the viewpoint of ensuring proper toner flowability. The number-average primary particle size of silica particle B may be 10 to 30 nm or 15 to 25 nm, from the viewpoint of ensuring proper toner flowability. The number-average primary particle size of silica particle C may be 6.5 to 12 nm or 7.0 to 10 nm, from the viewpoint of ensuring proper toner flowability.

[0033] The content of the silica particles A is not particularly limited, but from the viewpoint of improving printing performance or shelf life, it is preferably 0.30 parts by mass or more, more preferably 0.50 parts by mass or more, per 100 parts by mass of colored resin particles. On the other hand, from the viewpoint of suppressing deterioration of printing performance by suppressing the release of silica particles A from the surface of toner particles, the content of the silica particles A per 100 parts by mass of colored resin particles is preferably 2.50 parts by mass or less, more preferably 2.00 parts by mass or less, and even more preferably 1.50 parts by mass or less. Furthermore, when the content of silica particles A is within the above range, it is easier to obtain toner with the desired fluidity.

[0034] The content of silica particles B is not particularly limited, but in order to suppress the decrease in toner fluidity and prevent deterioration of the toner's shelf life or durability, it is preferably 0.10 parts by mass or more, more preferably 0.30 parts by mass or more, and even more preferably 0.50 parts by mass or more, per 100 parts by mass of colored resin particles. On the other hand, in order to suppress the release of silica particles B from the surface of toner particles, prevent deterioration of charge characteristics, and prevent fogging, the content of silica particles B per 100 parts by mass of colored resin particles is preferably 2.00 parts by mass or less, more preferably 1.50 parts by mass or less, and even more preferably 1.00 part by mass or less. Furthermore, when the content of silica particles B is within the above range, it is easier to obtain toner with the desired fluidity.

[0035] The content of silica particles C is not particularly limited, but in order to suppress the decrease in toner fluidity and prevent deterioration of toner shelf life, it is preferably 0.10 parts by mass or more, more preferably 0.15 parts by mass or more, and even more preferably 0.20 parts by mass or more, per 100 parts by mass of colored resin particles. On the other hand, in order to suppress the release of silica particles C from the surface of toner particles, thereby suppressing deterioration of charge characteristics and preventing fogging, it is preferably 1.50 parts by mass or less, more preferably 1.00 parts by mass or less, even more preferably 0.80 parts by mass or less, and even more preferably 0.60 parts by mass or less. Furthermore, when the content of silica particles C is within the above range, it is easier to obtain toner with the desired fluidity.

[0036] Various commercially available silica particles can be used as silica particles A, B, and C. Examples of silica particle A include VPNA50H (product name, average primary particle size: 40 nm) manufactured by Nippon Aerosil Co., Ltd.; H05TA (product name, average primary particle size: 50 nm) manufactured by Wacker Corporation; and others. Examples of silica particle B include NA50Y (product name, average primary particle size: 35 nm) manufactured by Nippon Aerosil Co., Ltd.; MSP-012 (product name, average primary particle size: 16 nm) manufactured by Teika Corporation; and TG-7120 (product name, average primary particle size: 20 nm) manufactured by Cabot Corporation. Examples of silica particles C include HDK2150 (product name, average primary particle size: 12 nm) from Clariant Corporation; R504 (product name, average primary particle size: 12 nm) and RA200HS (product name, average primary particle size: 12 nm) from Nippon Aerosil Co., Ltd.; MSP-013 (product name, average primary particle size: 12 nm) from Teika Corporation; and TG-820F (product name, average primary particle size: 7 nm) from Cabot Corporation.

[0037] The positively charged toner of this disclosure may contain metal soap fine particles D as an external additive. This makes it easier to obtain a toner with the desired fluidity. Furthermore, when metal soap fine particles D are included as an external additive, filming on the photoreceptor is less likely to occur, stable charging is imparted to the toner particles over time, and even when printing many sheets continuously, deterioration of image quality due to fogging, etc., is less likely to occur, and in particular, a toner that does not deteriorate in image quality even in a high temperature and high humidity environment (HH environment) can be obtained. In order to easily exhibit the effects of such metal soap fine particles D, the number-average primary particle size of the metal soap fine particles D is preferably 0.3 μm or more, more preferably 0.4 μm or more, even more preferably 0.5 μm or more, while preferably 1.0 μm or less, more preferably 0.9 μm or less, and even more preferably 0.8 μm or less.

[0038] As the metal soap fine particles D, it is preferable to use fatty acid metal salt particles. The fatty acid moiety (R-COO) of the fatty acid metal salt particles － Examples of fatty acids that induce ) include those similar to those that induce the fatty acid moiety of the fatty acid alkali metal salt used in strontium titanate particles, and fatty acids that are preferably used in fatty acid alkali metal salts can also be preferably used in fatty acid metal salt particles which are metal soap fine particles D.

[0039] The metal contained in the fatty acid metal salt particles may be an alkali metal, an alkaline earth metal, or a metal element of Group 12 of the periodic table, such as Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Zn, etc. Among these, alkaline earth metals or metal elements of Group 12 of the periodic table are preferred, at least one selected from the group consisting of Mg and Zn is more preferred, and Zn is even more preferred.

[0040] Various commercially available fatty acid metal salt particles can be used, for example, SPZ-100F (product name, zinc stearate particles, number average primary particle size: 0.5 μm) and SPX-100F (product name, magnesium stearate particles, number average primary particle size: 0.72 μm) manufactured by Sakai Chemical Industry Co., Ltd.

[0041] The content of metal soap fine particles D is not particularly limited, but in order to suppress toner aggregation and prevent toner ejection, and to suppress the decrease in electrostatic charge in high temperature and high humidity environments and prevent fogging, it is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.03 parts by mass or more, and even more preferably 0.04 parts by mass or more, per 100 parts by mass of colored resin particles. On the other hand, in order to suppress deterioration of toner fixation due to an excessive amount of external additive, and to suppress the release of metal soap fine particles D from the surface of toner particles and prevent a decrease in toner fluidity, the content of metal soap fine particles D per 100 parts by mass of colored resin particles is preferably 0.30 parts by mass or less, more preferably 0.25 parts by mass or less, and even more preferably 0.20 parts by mass or less. Furthermore, when the content of metal soap fine particles D is within the above range, it is easier to obtain toner with the desired fluidity. Note that metal soap fine particles D can be used alone or in combination of two or more types.

[0042] The positively charged toner of this disclosure may contain silicone resin particles as an external additive. This improves the toner's fluidity, reduces filming on the photoreceptor, imparts stable charging to the toner particles over time, and reduces image quality degradation due to fogging, etc., even when printing many pages continuously. The silicone resin particles are organopolysiloxane particles having a three-dimensional network structure, such as polymethylsilsesquioxane particles. Furthermore, it is preferable that the silicone resin particles are hydrophobized silicone resin particles. Examples of hydrophobizing agents used for the silicone resin particles include those similar to those that can be used for the inorganic fine particles.

[0043] The number-average primary particle size of the silicone resin particles is not particularly limited, but is preferably 0.05 to 1.00 μm, more preferably 0.07 to 0.50 μm, and even more preferably 0.08 to 0.30 μm. When the number-average primary particle size of the silicone resin particles is within the above range, the toner can have appropriate charging characteristics under a wide range of temperature and humidity conditions.

[0044] The content of the silicone resin particles is not particularly limited, but is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of colored resin particles, while preferably 2 parts by mass or less, more preferably 1 part by mass or less, and even more preferably 0.5 parts by mass or less. If the content of the silicone resin particles is above the lower limit, the fluidity of the toner tends to improve, so toner ejection is easily suppressed, and the occurrence of filming or fogging is suppressed. If the content of the silicone resin particles is below the upper limit, the release of the silicone resin particles from the surface of the toner particles is suppressed, thereby suppressing deterioration of printing performance or the occurrence of fogging. The silicone resin particles can be used individually or in combination of two or more types.

[0045] External additive treatment, which involves attaching an external additive to the surface of colored resin particles, can be carried out by known methods and is not particularly limited. External additive treatment can be carried out using a mixer capable of mixing and stirring, such as a Henschel mixer (trade name, manufactured by Mitsui Mining Co., Ltd.), an FM mixer (trade name, manufactured by Nippon Coke Industries Co., Ltd.), a Super mixer (trade name, manufactured by Kawada Manufacturing Co., Ltd.), a Q mixer (trade name, manufactured by Nippon Coke Industries Co., Ltd.), a Mechanofusion System (trade name, manufactured by Hosokawa Micron Corporation), and a Mechano Mill (trade name, manufactured by Okada Seikou Co., Ltd.).

[0046] In this disclosure, the number-average primary particle size is determined by first measuring the particle size of each individual particle using a transmission electron microscope (TEM) or scanning electron microscope (SEM). The particle sizes of 30 or more particles are measured, and the average value is taken as the number-average primary particle size of that particle. If the particle shape is non-spherical and the major and minor axes can be determined by observation using a TEM or SEM, the major and minor axes are first measured for each individual particle. The major and minor axes of 30 or more particles are measured in this manner, and the average value of each is taken as the average major or average minor axis of that particle. The sum of the calculated average major and average minor axes is divided by 2 to obtain the number-average primary particle size of that particle.

[0047] In the positively charged toner of this disclosure, the total content of the external additive per 100 parts by mass of colored resin particles is not particularly limited, but is preferably 1.5 parts by mass or more and 6.0 parts by mass or less, and more preferably 2.0 parts by mass or more and 4.0 parts by mass or less. If the content of the external additive is above the lower limit, the fluidity of the toner is improved, and if it is below the upper limit, deterioration of the toner's transferability is suppressed.

[0048] 1-2. Colored Resin Particles The colored resin particles contained in the positively charged toner of this disclosure are the mother particles of the toner and are not particularly limited as long as they are colored resin particles that produce a positively charged toner when combined with the external additives described above. The colored resin particles contained in the positively charged toner of this disclosure usually contain a binder resin, a colorant and a charge control agent, and may further contain other additives such as a softener, a polar resin and a styrene-based thermoplastic elastomer as needed. The colored resin particles may also be core-shell type colored resin particles having a core layer containing a binder resin and a shell layer containing a resin different from the binder resin.

[0049] [Binding Resin] As the binding resin, resins that have been widely used in toners in the past can be used, for example, styrene-acrylic resins, polystyrene, polyester resins, and epoxy resins. Among these, styrene-acrylic resins are preferred because they provide a good balance between the low-temperature fixing properties and heat-resistant storage properties of positively charged toners. The styrene-acrylic resin may be, for example, a copolymer of an aromatic vinyl monomer and a (meth)acrylate monomer. The copolymer may be further copolymerized with other monomers different from the aromatic vinyl monomer or the (meth)acrylate monomer, to the extent that it does not impair the purpose of this disclosure. The (meth)acrylate monomer is at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters. In this disclosure, the styrene-acrylic resin used as the binding resin is distinguished from a charge-controlling resin in that the amount of functional groups is less than 0.1% by mass, and is distinguished from a polar resin in that the acid value is less than 0.5 mgKOH / g.

[0050] Furthermore, although not particularly limited, in order to achieve a good balance between the low-temperature fixing properties and heat-resistant storage properties of the positively charged toner, the content of styrene-acrylic resin in 100 parts by mass of the total amount of binder resin may be, for example, 90 parts by mass or more, 95 parts by mass or more, or 99 parts by mass or more.

[0051] In the positively charged toner of this disclosure, the styrene-acrylic resin used as the binder resin may be, for example, a polymer of the polymerizable monomers described below. Furthermore, although not particularly limited, in order to achieve a good balance between the low-temperature fixing properties and heat-resistant storage properties of the positively charged toner, the content of the polymer of the polymerizable monomers described below in 100 parts by mass of the total amount of binder resin may be, for example, 90 parts by mass or more, 95 parts by mass or more, or 99 parts by mass or more.

[0052] (Polymerizable Monomers) In this disclosure, a polymerizable monomer refers to a monomer having polymerizable functional groups. It is preferable to use a monovinyl monomer as the main component of the polymerizable monomer. That is, it is preferable that the binder resin contained in the colored resin particles is a polymer of a polymerizable monomer containing a monovinyl monomer. Examples of monovinyl monomers include aromatic monovinyl compounds such as styrene and styrene derivatives such as vinyltoluene and α-methylstyrene; acrylic acid and methacrylic acid; acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and dimethylaminoethyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and dimethylaminoethyl methacrylate; nitrile compounds such as acrylonitrile and methacrylonitrile; amide compounds such as acrylamide and methacrylamide; and olefins such as ethylene, propylene, and butylene. These monovinyl monomers can be used individually or in combination of two or more. Among these, styrene, styrene derivatives, acrylic acid esters, and methacrylic acid esters are preferably used as monovinyl monomers in order to achieve a good balance between the low-temperature fixability and heat-resistant storage properties of positively charged toners. Among acrylic acid esters, at least one selected from the group consisting of n-butyl acrylate, propyl acrylate, and 2-ethylhexyl acrylate is preferred, and among methacrylic acid esters, at least one selected from the group consisting of n-butyl methacrylate, propyl methacrylate, and 2-ethylhexyl methacrylate is preferred. Furthermore, for the same reasons as above, it is preferable that the monovinyl monomers include a combination of at least one selected from the group consisting of styrene and styrene derivatives and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters, and it is more preferable that the monovinyl monomers include a combination of styrene and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters.Furthermore, the styrene content in 100 parts by mass of the total monovinyl monomer is not particularly limited, but for the same reasons as above, it is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, while preferably 90 parts by mass or less, more preferably 80 parts by mass or less. Also, for the same reasons as above, the total mass of monovinyl monomers, such as styrene, styrene derivatives, acrylic acid esters, and methacrylic acid esters, in 100 parts by mass of the total polymerizable monomer may be 90 parts by mass or more, 95 parts by mass or more, or 99 parts by mass or more. Furthermore, for the same reasons as above, the monovinyl monomer contains at least one selected from the group consisting of styrene and styrene derivatives, and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters, and the ratio (M1:M2) of the total mass of styrene and styrene derivatives (M1) to the total mass of acrylic acid esters and methacrylic acid esters (M2) is preferably in the range of 50:50 to 90:10, and more preferably in the range of 60:40 to 80:20.

[0053] The content of monovinyl monomer in 100% by mass of polymerizable monomer is not particularly limited, but in order to achieve a good balance between the low-temperature fixing properties and heat-resistant storage properties of the positively charged toner, it may be, for example, 95% by mass or more, 98% by mass or more, or 99% by mass or more. The polymerizable monomer may consist of monovinyl monomer, but the content of monovinyl monomer in 100% by mass of polymerizable monomer may be, for example, 99.9% by mass or less, 99.7% by mass or less, or 99.5% by mass or less.

[0054] As polymerizable monomers, it is preferable to use any crosslinkable polymerizable monomer together with a monovinyl monomer to improve the hot offset and storage life of positively charged toners. A crosslinkable polymerizable monomer is a monomer having two or more polymerizable functional groups. Examples of crosslinkable polymerizable monomers include aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, and their derivatives; ester compounds in which two or more carboxylic acids having carbon-carbon double bonds are ester-bonded to an alcohol having two or more hydroxyl groups, such as ethylene glycol dimethacrylate and diethylene glycol dimethacrylate; other divinyl compounds such as N,N-divinylaniline and divinyl ether; compounds having three or more vinyl groups; and so on. These crosslinkable polymerizable monomers can be used individually or in combination of two or more. Of these, aromatic divinyl compounds are preferably used as crosslinkable polymerizable monomers, and divinylbenzene is particularly preferably used. When the polymerizable monomer contains the crosslinkable polymerizable monomer, the content of the crosslinkable polymerizable monomer is not particularly limited, but is usually 0.1 to 5 parts by mass, preferably 0.3 to 2 parts by mass, and more preferably 0.5 to 1 part by mass, per 100 parts by mass of monovinyl monomer.

[0055] Furthermore, using macromonomers as part of the polymerizable monomer is preferable because it provides a good balance between the storage properties and low-temperature fixability of the positively charged toner. Macromonomers are oligomers or polymers with a number average molecular weight of typically 1,000 to 30,000 and a high reactivity, having polymerizable carbon-carbon unsaturated double bonds at the ends of their molecular chains. Examples of the above macromonomers include styrene macromonomers, styrene-acrylonitrile macromonomers, polyacrylic acid ester macromonomers, and polymethacrylic acid ester macromonomers. Among these, at least one selected from the group consisting of polyacrylic acid ester macromonomers and polymethacrylic acid ester macromonomers is preferably used. Examples of acrylic acid esters used in polyacrylic acid ester macromonomers include those similar to those usable as monovinyl monomers, and examples of methacrylic acid esters used in polymethacrylic acid ester macromonomers include those similar to those usable as monovinyl monomers. Among the macromonomers mentioned above, it is preferable to appropriately select and use those that, when included in the polymerizable monomer, result in a higher glass transition temperature (Tg) of the resulting binder resin compared to when they are not included. Commercially available macromonomers may also be used. Examples of commercially available macromonomers include the macromonomer series AA-6, AS-6, AN-6S, AB-6, AW-6S, etc., manufactured by Toagosei Co., Ltd. Each of the macromonomers can be used individually or in combination of two or more. When the polymerizable monomer contains the macromonomer, the content of the macromonomer is not particularly limited, but is preferably 0.03 to 5 parts by mass, more preferably 0.05 to 2 parts by mass, even more preferably 0.1 to 1.5 parts by mass, and even more preferably 0.3 to 1 part by mass, per 100 parts by mass of the monovinyl monomer.

[0056] In the positively charged toner of this disclosure, the content of the binder resin is not particularly limited, but in order to achieve a good balance between the low-temperature fixing properties and heat-resistant storage properties of the positively charged toner, it may be, for example, 60 to 95 parts by mass, 65 to 90 parts by mass, or 70 to 85 parts by mass per 100 parts by mass of colored resin particles.

[0057] [Colorants] As colorants, conventional colorants used in toners can be appropriately selected and used, and are not particularly limited. When producing color toner, white, black, cyan, yellow, or magenta colorants can be used. As a white colorant, there are no particular limitations, but titanium dioxide can be preferably used from the viewpoint of opacity. In addition to titanium dioxide, other white colorants include, for example, zinc oxide, antimony white, zinc sulfide, barium sulfate, etc., and these may be used in combination with titanium dioxide. As for titanium dioxide, any crystalline form of anatase, rutile, or brookite can be used. As black colorants, for example, carbon black, titanium black, and magnetic powders such as zinc iron oxide and nickel iron oxide can be used. As cyan colorants, for example, phthalocyanine pigments such as copper phthalocyanine pigment and its derivatives, cyan pigments such as anthraquinone pigment, and cyan dyes can be used. Specifically, for example, C.I. Examples include Pigment Blue 2, 3, 6, 15, 15:1, 15:2, 15:3, 15:4, 16, 17:1, 60; C.I. Solvent Blue 70, etc. As yellow colorants, for example, azo pigments such as monoazo pigments and disazo pigments, yellow pigments such as condensed polycyclic pigments, and yellow dyes can be used. Specifically, examples include C.I. Pigment Yellow 3, 12, 13, 14, 15, 17, 62, 65, 73, 74, 83, 93, 97, 120, 138, 155, 180, 181, 185, 186, 213, 214; C.I. Solvent Yellow 98, 162, etc. Examples of magenta colorants that can be used include azo pigments such as monoazo pigments and disazo pigments, magenta pigments such as condensed polycyclic pigments such as quinacridone pigments, and magenta dyes.Specifically, for example, C.I. Pigment Red 31, 48, 57: 1, 58, 60, 63, 64, 68, 81, 83, 87, 88, 89, 90, 112, 114, 122, 123, 144, 146, 149, 150, 163, 170, 184, 185, 187, 202, 206, 207, 209, 237, 238, 251, 254, 255, 269; C.I. Pigment Violet 19; C.I. Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 81, 82, 83, 84, 100, 109, 121; C.I. Disperse Red 9; C.I. Examples include Solvent Violet 8, 13, 14, 21, 27; C.I. Disperse Violet 1; C.I. Basic Red 1, 2, 9, 12, 13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 34, 35, 36, 37, 38, 39, 40; and C.I. Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27, 28. These colorants can be used individually or in combination of two or more.

[0058] In the positively charged toner of this disclosure, the content of the colorant is not particularly limited, but from the viewpoint of print density and suppression of deterioration of toner fixation, it may be, for example, 5 to 15 parts by mass or 7 to 13 parts by mass per 100 parts by mass of binder resin. Furthermore, the content of the colorant per 100 parts by mass of the polymerizable monomer may be, for example, 5 to 15 parts by mass or 7 to 13 parts by mass. Furthermore, the content of the colorant per 100 parts by mass of the monovinyl monomer may be, for example, 5 to 15 parts by mass or 7 to 13 parts by mass.

[0059] [Charge Control Agent] The charge control agent typically includes a positive charge control agent. This improves the positive charge properties of the toner. While there are no particular limitations, any positive charge control agent commonly used for toners can be used as the positive charge control agent. However, a polymer-type positive charge control agent (charge control resin) is preferred because it has high compatibility with the binder resin and can impart stable charge properties (charge stability) to the toner particles.

[0060] As a positively charged charge control resin, for example, a copolymer (which may be referred to as a "functional group-containing copolymer" in this disclosure) containing a monomer (which may be referred to as a "functional group-containing monomer" in this disclosure) that contains a functional group that imparts positive charge properties can be used. For example, a functional group-containing copolymer containing a functional group such as an amino group, a quaternary ammonium group, or a quaternary ammonium salt can be used. Examples include polyamine resins, quaternary ammonium group-containing copolymers, and quaternary ammonium salt-containing copolymers. These charge control resins can be used individually or in combination of two or more.

[0061] The glass transition temperature (Tg) of the above-mentioned charge-controlling resin is not particularly limited, but may be, for example, 60 to 90°C, 65 to 85°C, or 70 to 80°C. When the Tg of the charge-controlling resin is within the above range, a good balance is achieved between the toner's storage properties and its fixation properties. In this disclosure, the glass transition temperature (Tg) can be determined, for example, in accordance with ASTM D3418-82. Specifically, the sample is heated at a heating rate of 10°C / min using a differential scanning calorimeter (e.g., Seiko Electronics Industries, Ltd.: SSC5200), and the temperature at which the maximum endothermic peak is observed in the DSC curve obtained during this process can be defined as the glass transition temperature.

[0062] The weight-average molecular weight (Mw) of the above-mentioned charge-controlling resin is not particularly limited, but may be, for example, 5,000 to 30,000, 10,000 to 25,000, or 15,000 to 23,000. If the weight-average molecular weight (Mw) of the charge-controlling resin is above the lower limit, a decrease in the storage life and print durability of the toner can be suppressed, and if it is below the upper limit, a decrease in the fixation performance of the toner can be suppressed. Furthermore, if the weight-average molecular weight (Mw) of the charge-controlling resin is within the above range, the charge-controlling resin can be suitably dispersed in the binder resin, making it easier to obtain toner with a stable charge over time. In this disclosure, the weight-average molecular weight (Mw) is a polystyrene-equivalent value measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF).

[0063] In the electrostatic control resin, the content of functional group-containing monomer units is preferably 0.5 to 8% by mass, from the viewpoint of imparting the desired electrostatic properties to the toner. In this disclosure, the content of monomer units containing functional groups that impart electrostatic properties, i.e., the copolymerization ratio of monomers containing functional groups that impart electrostatic properties, out of 100% by mass of all monomer units in the electrostatic control resin, may be referred to as the "amount of functional groups." In the quaternary ammonium salt-containing copolymer preferably used as an electrostatic control agent in this disclosure, since the group containing the quaternary ammonium salt is a functional group that imparts positive electrostatic properties to the toner, the content of quaternary ammonium salt-containing monomer units out of 100% by mass, i.e., the copolymerization ratio of quaternary ammonium salt-containing monomers, may be simply referred to as the "amount of functional groups." The above amount of functional groups may be 1 to 5% by mass or 2 to 4% by mass, from the viewpoint of imparting the desired electrostatic properties to the toner or improving the dispersibility of the colorant.

[0064] In the positively charged toner of this disclosure, a quaternary ammonium salt-containing copolymer is preferably used as the charge control agent from the viewpoint of the toner's charging characteristics and printing performance. Here, the quaternary ammonium salt-containing copolymer is a copolymer containing monomer units containing a quaternary ammonium salt (quaternary ammonium salt-containing monomer), and may be, for example, a copolymer of a quaternary ammonium salt-containing monomer and another monomer copolymerizable with said monomer.

[0065] The quaternary ammonium salt contained in the above quaternary ammonium salt-containing copolymer is -NR ３ ＋ ・X － It is contained as a group having an ionic structure represented by . In this ionic structure, each of the three Rs is independently a hydrogen atom or a substituent such as an alkyl group. From the viewpoint of excellent effect in imparting positive charge to the toner, it is preferable that the three Rs are hydrogen atoms or linear, branched, or cyclic alkyl groups having 1 to 6 carbon atoms. X － -SO4 is a halogen ion, an alkyl group in which one hydrogen atom is substituted with a halogen ion, or a group in which at least one hydrogen atom may be substituted with a halogen atom.３ － , -PO ３ － Or -BO ３ － It is a hydrocarbon group having [a certain characteristic]. Examples of hydrocarbon groups include alkyl groups, aromatic hydrocarbon groups, and substituted aromatic hydrocarbon groups. － In particular, in the positively charged toner of this disclosure, in order to make it easier to maintain the amount of charge during continuous printing and suppress printing defects, at least one hydrogen atom may be substituted with a halogen atom, -SO ３ － It is preferably a hydrocarbon group having a hydrocarbon group, more preferably an aromatic sulfonic acid anion which may have at least one substituent selected from the group consisting of a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms and a halogen atom, and even more preferably a benzenesulfonic acid anion or a p-toluenesulfonic acid anion.

[0066] As a quaternary ammonium salt-containing copolymer, for example, a quaternary ammonium salt-containing styrene-acrylic resin can be preferably used. Examples of quaternary ammonium salt-containing styrene-acrylic resins include copolymers containing quaternary ammonium salt-containing monomer units, aromatic vinyl monomer units, and (meth)acrylate monomer units. Here, the aromatic vinyl monomer units and (meth)acrylate monomer units do not contain functional groups that impart electrostatic charge. The quaternary ammonium salt-containing styrene-acrylic resin may be further copolymerized with other monomers different from the quaternary ammonium salt-containing monomer, aromatic vinyl monomer, or (meth)acrylate monomer, to the extent that it does not impair the purpose of this disclosure. The content of the other monomer units is not particularly limited, but is usually 10% by mass or less, may be 5% by mass or less, or may be 1% by mass or less. The above quaternary ammonium salt-containing styrene-acrylic resin is preferred in the positively charged toner of this disclosure from the viewpoint of uniformly controlling the charge amount because it has high compatibility with the binder resin. From this perspective, among quaternary ammonium salt-containing styrene-acrylic resins, it is preferable that the quaternary ammonium salt-containing monomer units are quaternary ammonium salt-containing (meth)acrylate monomer units. Furthermore, from the viewpoint of dispersibility in polymerizable monomer compositions, it is preferable that the above-mentioned quaternary ammonium salt-containing copolymer dissolves in aromatic vinyl monomers.

[0067] Examples of quaternary ammonium salt-containing (meth)acrylate monomer units that are preferably contained in the above-mentioned quaternary ammonium salt-containing copolymer include structural units represented by the following formula [I].

[0068] [In the above formula [I], R １ R is a hydrogen atom or a methyl group, ２ R is a linear or branched alkylene group having 1 to 3 carbon atoms, in which at least one hydrogen atom may be substituted with a halogen atom. ３ ~R ５ Each is independently a hydrogen atom or a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms, and X －It may have a halogen ion, or at least one substituent selected from the group consisting of a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms, and a halogen atom, -SO ３ － , -PO ３ － Or -BO ３ － It is a benzene or naphthalene having either of the following properties.

[0069] X － -SO ３ － , -PO ３ － Or -BO ３ － It is a benzene or naphthalene having either of the following properties. － For example, an aromatic sulfonate anion having the above substituent may be used, as it helps maintain the toner charge during continuous printing and reduces the likelihood of printing defects. Examples of the above aromatic sulfonate anion include benzenesulfonate anion and p-toluenesulfonate anion.

[0070] Specific examples of structural units represented by the above formula [I] include structural units corresponding to quaternary ammonium salt-containing monomers such as N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium chloride, 2-(methacryloyloxy)ethyltrimethylammonium chloride (DMC; dimethylaminoethylmethyl chloride methacrylate), 2-(methacryloyloxy)-N-benzyl-N,N-dimethylethaneammonium chloride (DML; dimethylaminoethylbenzyl chloride methacrylate), and N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium p-toluenesulfonate, 2-(methacryloyloxy)ethyltrimethylammonium p-toluenesulfonate, and 2-(methacryloyloxy)-N-benzyl-N,N-dimethylethaneammonium p-toluenesulfonate. Among these, the structural unit corresponding to N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium p-toluenesulfonate is preferred. Furthermore, the structural unit corresponding to a monomer is a structural unit in which the carbon-carbon double bond of the monomer is replaced by a carbon-carbon single bond through polymerization.

[0071] In the above-mentioned quaternary ammonium salt-containing styrene-acrylic resin, the copolymerization ratio of aromatic vinyl monomer and (meth)acrylate monomer is not particularly limited, but from the viewpoint of solubility in polymerizable monomers and dispersibility in binder resins, the mass ratio of (meth)acrylate monomer units to aromatic vinyl monomer units ((meth)acrylate monomer units / aromatic vinyl monomer units) is preferably 0.05 to 0.35, more preferably 0.10 to 0.30, and even more preferably 0.15 to 0.25.

[0072] Furthermore, from the viewpoint of improving print density, it is also preferable to include a combination of copolymer A and copolymer B as the charge control resin. Here, copolymer A and copolymer B are functional group-containing copolymers with different amounts of functional groups, with copolymer A having more functional groups than copolymer B. When copolymer A, which has a relatively large amount of functional groups, and copolymer B, which has a relatively small amount of functional groups, are included in the colored resin particles as a charge control resin, it is possible to improve the dispersibility of the colorant while imparting the desired charge toner. As a result, the colorant can be included at a high concentration, thereby improving print density. When copolymer A and copolymer B are used in combination as charge control agents, due to the difference in the amount of functional groups, copolymer B is thought to be biased towards the relatively central side of the colored resin particles, while copolymer A is biased towards the surface side of the colored resin particles. Copolymer A has a higher charge imparting effect because it has a larger amount of functional groups than copolymer B, and because it is biased towards the surface side of the colored resin particles, the charge properties of the toner are thought to be mainly influenced by copolymer A. On the other hand, copolymer B also exhibits a charge imparting effect, but is thought to have a high effect in dispersing the colorant within the colored resin particles. It is presumed that the interaction between copolymer A and copolymer B imparts the desired electrostatic properties to the toner and improves the dispersibility of the colorant.

[0073] The amount of functional groups in copolymer A is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 8% by mass or less, and even more preferably 6% by mass or less, from the standpoint of imparting the desired electrostatic properties to the toner and improving the dispersibility of the colorant, as a lower limit. The amount of functional groups in copolymer B is preferably 0.5% by mass or more, more preferably 0.7% by mass or more, and preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less, from the standpoint of imparting the desired electrostatic properties to the toner and improving the dispersibility of the colorant, as a lower limit.

[0074] The difference between the amount of functional groups in copolymer A and the amount of functional groups in copolymer B (amount of functional groups in copolymer A - amount of functional groups in copolymer B) is preferably 0.5 to 5% by mass, more preferably 1 to 3% by mass, from the standpoint of imparting the desired electrostatic properties to the toner and improving the dispersibility of the colorant.

[0075] Furthermore, from the viewpoint of imparting the desired electrostatic properties to the toner and improving the dispersibility of the colorant, it is preferable that the functional groups contained in copolymer A and copolymer B have the same structure, and more preferably that they are quaternary ammonium salt-containing groups. Also, from a similar viewpoint, it is preferable that each of copolymer A and copolymer B is a quaternary ammonium salt-containing copolymer, and more preferably that both are quaternary ammonium salt-containing styrene-acrylic resins.

[0076] In a toner containing a combination of copolymer A and copolymer B, the ratio of the content of copolymer A to the content of copolymer B (content of copolymer A / content of copolymer B) is not particularly limited, but from the viewpoint of imparting the desired electrostatic properties to the toner, improving the dispersibility of the colorant, and improving the heat resistance of the toner, it may be, for example, 0.5 to 10.0, 0.8 to 5.0, or 1.0 to 3.0. If the above ratio is above the lower limit, the toner quality can be easily controlled, and if it is below the upper limit, the dispersibility of the colorant is particularly improved, making it easy to improve the print density.

[0077] Furthermore, other positively charged charge control agents include nigrosine dyes, quaternary ammonium salts, triaminotriphenylmethane compounds, and imidazole compounds. On the other hand, from the viewpoint of the charging characteristics of the positively charged toner of this disclosure, it is preferable that the content of the positively charged charge control resin in 100% by mass of the charge control agent contained in the positively charged toner of this disclosure is 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. From the same viewpoint as above, it is preferable that the content of the quaternary ammonium salt-containing copolymer in 100% by mass of the charge control agent contained in the positively charged toner of this disclosure is 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. The positively charged charge control resin can be used alone or in combination of two or more types. The quaternary ammonium salt-containing copolymer can also be used alone or in combination of two or more types.

[0078] In the positively charged toner of this disclosure, the content of the charge control agent is not particularly limited, but may be, for example, 0.1 to 10 parts by mass, 0.3 to 5 parts by mass, or 0.6 to 3 parts by mass per 100 parts by mass of binder resin. Furthermore, the content of the charge control agent per 100 parts by mass of polymerizable monomer may be, for example, 0.1 to 10 parts by mass, 0.3 to 5 parts by mass, or 0.6 to 3 parts by mass. Furthermore, the content of the charge control agent per 100 parts by mass of monovinyl monomer may be, for example, 0.1 to 10 parts by mass, 0.3 to 5 parts by mass, or 0.6 to 3 parts by mass. When the content of the charge control agent is within the above range, the charging characteristics and printing performance of the positively charged toner of this disclosure tend to be good. Furthermore, when the content of the charge control agent is above the lower limit, fogging can be suppressed, while when it is below the upper limit, printing smudges can be suppressed.

[0079] [Softener] The colored resin particles may contain a softener. By including a softener, the release properties of the toner from the fixing roll during fixing can be improved. As a softener, any softener commonly used as a softener or release agent for toner can be used without particular limitations. Examples include low molecular weight polyolefin waxes and their modified waxes; petroleum waxes such as paraffin; mineral waxes such as ozokerite; synthetic waxes such as Fischer-Tropsch wax; ester waxes such as dipentaerythritol ester and carnauba wax; and so on. Among these, ester waxes are preferred in terms of improving the balance between the storage properties and low-temperature fixing properties of the toner, and synthetic ester waxes obtained by esterifying an alcohol and a carboxylic acid can be preferably used. The alcohol used in the ester wax may be a saturated aliphatic alcohol, an unsaturated aliphatic alcohol, or an aromatic alcohol, and may be a monohydric alcohol or a polyhydric alcohol. The carboxylic acid used in the ester wax may be a monocarboxylic acid or a polyhydric carboxylic acid, and a fatty acid that is a monocarboxylic acid is preferably used. The fatty acid may be a saturated fatty acid, an unsaturated fatty acid, or an aromatic fatty acid. Among ester waxes, monoester waxes are preferred because they are excellent at improving the low-temperature fixation of toners, while polyfunctional ester waxes are preferred because they are less prone to bleed-out. Examples of monoester waxes include behenyl palmitate (C １５ H ３１ -COO-C ２２ H ４５ ), behenyl stearate (C １７ H ３５ -COO-C ２２ H ４５ ), behenyl eicosanoate (C １９ H ３９ -COO-C ２２ H ４５ ), behenyl behenate (C ２１ H ４３ -COO-C ２２ H ４５ ), eicosyl palmitate (C １５ H３１ -COO-C ２０ H ４１ ), eicosyl stearate (C １７ H ３５ -COO-C ２０ H ４１ ), eicosyl eicosanoate (C １９ H ３９ -COO-C ２０ H ４１ ), eicosyl behenate (C ２１ H ４３ -COO-C ２０ H ４１ ), stearyl stearate (C １７ H ３５ -COO-C １８ H ３７ ), stearyl eicosanoate (C １９ H ３９ -COO-C １８ H ３７ ), stearyl behenate (C ２１ H ４３ -COO-C １８ H ３７ ), hexadecyl eicosanoate (C １９ H ３９ -COO-C １６ H ３３ ), hexadecyl behenate (C ２１ H ４３ -COO-C １６ H ３３Examples include the following. Among these, behenyl stearate, behenyl palmitate, behenyl behenate, and stearyl behenate are particularly preferred. As the polyfunctional ester wax, for example, at least one selected from the group consisting of pentaerythritol ester compounds, glycerin ester compounds, and dipentaerythritol ester compounds can be preferably used. Examples of such preferred polyfunctional ester waxes include pentaerythritol ester compounds such as pentaerythritol tetrapalmitate, pentaerythritol tetrabehenate, and pentaerythritol tetrastearate; glycerin ester compounds such as hexaglycerin tetrabehenate tetrapalmitate, hexaglycerin octabehenate, pentaglycerin heptabehenate, tetraglycerin hexabehenate, triglycerin pentabehenate, diglycerin tetrabehenate, and glycerin tripehenate; and dipentaerythritol ester compounds such as dipentaerythritol hexamiristate and dipentaerythritol hexapalmitate.

[0080] From the viewpoint of improving the balance between the storage properties and low-temperature fixing properties of the toner, the melting point of the softener is preferably in the range of 50 to 90°C, more preferably in the range of 60 to 85°C, and even more preferably in the range of 65 to 80°C. In this disclosure, the melting point of the softener is the transparent melting point.

[0081] In the positively charged toner of this disclosure, the content of the softener is not particularly limited, but in order to improve the balance between the storage properties and low-temperature fixing properties of the toner, the content of the softener per 100 parts by mass of the binder resin may be, for example, 1 to 30 parts by mass, 5 to 25 parts by mass, or 8 to 20 parts by mass. Also, the content of the softener per 100 parts by mass of the polymerizable monomer may be, for example, 1 to 30 parts by mass, 5 to 25 parts by mass, or 8 to 20 parts by mass. Also, the content of the softener per 100 parts by mass of the monovinyl monomer may be, for example, 1 to 30 parts by mass, 5 to 25 parts by mass, or 8 to 20 parts by mass. The softener can be used alone or in combination of two or more types.

[0082] [Polar Resin] The colored resin particles may contain polar resin. By including polar resin in the colored resin particles, the heat resistance and print durability of the toner can be improved. The polar resin tends to be unevenly distributed on the surface side of the colored resin particles. The polar resin is unevenly distributed on the surface side of the colored resin particles, reinforcing the particle surface and acting as a shell. As a result, even when using binder resins and softeners (release agents) with high low-temperature fixation properties, the toner can have excellent heat resistance. In addition, the print durability of the toner is improved because the surface of the colored resin particles becomes less prone to deterioration.

[0083] As the polar resin, an acidic group-containing copolymer is preferably used, and among these, an acrylate copolymer containing an acidic group is preferred. As an acrylate copolymer containing an acidic group, for example, a copolymer of (meth)acrylic acid ester and (meth)acrylic acid is preferably used. The copolymer of (meth)acrylic acid ester and (meth)acrylic acid is a copolymer of at least one selected from the group consisting of acrylic acid ester and methacrylic acid ester and at least one selected from the group consisting of acrylic acid and methacrylic acid. Examples of such copolymers include a copolymer of acrylic acid ester and acrylic acid, a copolymer of acrylic acid ester and methacrylic acid, a copolymer of methacrylic acid ester and methacrylic acid, a copolymer of acrylic acid ester, methacrylic acid ester and acrylic acid, and a copolymer of acrylic acid ester, methacrylic acid ester and methacrylic acid. Of these, the copolymer of acrylic acid ester, methacrylic acid ester and acrylic acid is preferred.

[0084] Examples of the (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, sec-pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, neohexyl (meth)acrylate, sec-hexyl (meth)acrylate, and tert-hexyl (meth)acrylate. Among the acrylic acid esters, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, and n-butyl acrylate are preferred, and ethyl acrylate and n-butyl acrylate are more preferred. Among the methacrylate esters, methyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, and n-butyl methacrylate are preferred, with methyl methacrylate being more preferred.

[0085] The mass ratio of each monomer unit in the acrylate copolymer is preferably adjusted to satisfy the acid value, weight-average molecular weight Mw, and glass transition temperature Tg described later. The content of (meth)acrylic acid units in 100% by mass of all monomer units constituting the acrylate copolymer is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more as a lower limit, and preferably 1.0% by mass or less, more preferably 0.6% by mass or less, and even more preferably 0.5% by mass or less as an upper limit. The content of (meth)acrylic acid ester units in 100% by mass of all monomer units constituting the acrylate copolymer is preferably 99.0% by mass or more, more preferably 99.4% by mass or more, and even more preferably 99.5% by mass or more as a lower limit, and preferably 99.95% by mass or less, more preferably 99.9% by mass or less, and even more preferably 99.7% by mass or less as an upper limit.

[0086] The acrylate copolymer may contain other monomer units different from (meth)acrylic acid ester units or (meth)acrylic acid units, to the extent that it does not impair the purpose of this disclosure. Examples of such other monomers include aromatic vinyl compounds, nitrile compounds, and amide compounds, which are exemplified in the monovinyl monomers constituting the binder resin. In the acrylate copolymer, the content of the other monomer units is preferably 10 parts by mass or less, more preferably 2 parts by mass or less, and most preferably 0 parts by mass, per 100 parts by mass of (meth)acrylic acid ester units.

[0087] The acid value of the polar resin is not particularly limited, but is preferably 0.5 mg KOH / g or more, more preferably 1.0 mg KOH / g or more, and even more preferably 2.0 mg KOH / g or more. On the other hand, it is preferably 5.0 mg KOH / g or less, more preferably 4.0 mg KOH / g or less, and even more preferably 3.0 mg KOH / g or less. When the acid value of the polar resin is within the above range, it is easy to obtain a toner with excellent low-temperature fixability, heat resistance, and print durability. In this disclosure, the acid value of the resin is measured in accordance with JIS K 0070.

[0088] The weight-average molecular weight (Mw) of the polar resin is not particularly limited, but is preferably 6,000 or more, more preferably 7,000 or more, and even more preferably 9,000 or more, while preferably 50,000 or less, more preferably 45,000 or less, and even more preferably 40,000 or less. When the weight-average molecular weight (Mw) of the polar resin is within the above range, the low-temperature fixability, heat resistance, and print durability of the positively charged toner of this disclosure can be improved.

[0089] The glass transition temperature Tg of the polar resin is not particularly limited, but is preferably 60°C or higher, more preferably 65°C or higher, and even more preferably 70°C or higher, while preferably 85°C or lower, more preferably 80°C or lower, and even more preferably 77°C or lower. When the glass transition temperature Tg of the polar resin is within the above range, the low-temperature fixability, heat resistance, and print durability of the positively charged toner of this disclosure can be improved.

[0090] In the positively charged toner of this disclosure, the content of the polar resin is not particularly limited, but the content of the polar resin per 100 parts by mass of the binder resin may be, for example, 0.2 to 5 parts by mass, 0.5 to 3 parts by mass, or 0.7 to 2 parts by mass. Also, the content of the polar resin per 100 parts by mass of the polymerizable monomer may be, for example, 0.2 to 5 parts by mass, 0.5 to 3 parts by mass, or 0.7 to 2 parts by mass. Also, the content of the polar resin per 100 parts by mass of the monovinyl monomer may be, for example, 0.2 to 5 parts by mass, 0.5 to 3 parts by mass, or 0.7 to 2 parts by mass. When the content of the polar resin is above the lower limit, the decrease in print durability is suppressed, and when it is below the upper limit, the charge amount of the toner tends to be appropriate, in particular, the decrease in the charge amount of the toner is suppressed, and the decrease in production stability and the decrease in low-temperature fixability are suppressed.

[0091] The polar resin can be a commercially available product, but it can also be produced by known polymerization methods such as solution polymerization, aqueous solution polymerization, ionic polymerization, high-temperature high-pressure polymerization, and suspension polymerization. A typical example of a method for producing the polar resin is as follows. Note that the method for producing the polar resin is not limited to the following typical example. First, a solvent is appropriately added to the reaction vessel, the inside of the reaction vessel is replaced with an inert atmosphere, the temperature is raised, and the raw material monomer is added to the reaction vessel. At this time, it is preferable to add a polymerization initiator at the same time. It is also preferable to gradually add a mixture of the raw material monomer and polymerization initiator dropwise into the reaction vessel. Next, the temperature is raised to a temperature at which polymerization proceeds, and polymerization is started. After polymerization is complete, the solvent is appropriately removed by distillation to obtain the desired polar resin.

[0092] [Styrene-based thermoplastic elastomer] The colored resin particles may contain a styrene-based thermoplastic elastomer. The styrene-based thermoplastic elastomer can improve the toner's fixation while maintaining the toner's heat resistance temperature. Here, styrene-based thermoplastic elastomer refers to a copolymer of a styrene-based monomer and at least one other monomer selected from the group consisting of monoolefins and diolefins that can copolymerize with the styrene-based monomer, such as a random, block, or graft copolymer, and hydrogenated products of these copolymers.

[0093] Examples of styrene-based thermoplastic elastomers include styrene-butadiene-styrene type block copolymers, styrene-butadiene type block copolymers, styrene-isoprene-styrene type block copolymers, styrene-isoprene type block copolymers, styrene-butadiene-isoprene-styrene type block copolymers and their hydrogenated derivatives; styrene-ethylene-butylene-styrene type block copolymers, styrene-ethylene-propylene-styrene type block copolymers, and styrene-ethylene-ethylene-propylene-styrene type block copolymers. Among these styrene-based thermoplastic elastomers, styrene-isoprene-styrene type block copolymers are preferred from the viewpoint of optimizing the balance between toner storage and low-temperature fixing properties.

[0094] The styrene content in the above-mentioned styrene-based thermoplastic elastomer is preferably 15 to 70% by mass, more preferably 15 to 60% by mass, and even more preferably 20 to 40% by mass. When the styrene content is above the lower limit, the decrease in toner fixability is suppressed. On the other hand, when the styrene content is below the upper limit, the decrease in toner storage life is suppressed.

[0095] The weight-average molecular weight Mw of the above-mentioned styrene-based thermoplastic elastomer is not particularly limited, but is preferably 50,000 to 350,000, and more preferably 80,000 to 250,000, from the standpoint of being excellent in improving the fixability of the toner while maintaining the heat resistance temperature of the toner.

[0096] Commercially available styrene-based thermoplastic elastomers can be used. Examples of commercially available styrene-based thermoplastic elastomers include the Quintac® series manufactured by Nippon Zeon Co., Ltd. and the Septon® series manufactured by Kuraray Co., Ltd.

[0097] In the positively charged toner of this disclosure, the content of the styrene-based thermoplastic elastomer is preferably adjusted to achieve a good balance between the low-temperature fixability and storage properties of the toner. While not particularly limited, the content of the styrene-based thermoplastic elastomer per 100 parts by mass of the binder resin may be, for example, 0.5 to 10 parts by mass, 1 to 8 parts by mass, or 2 to 6 parts by mass. Furthermore, the content of the styrene-based thermoplastic elastomer per 100 parts by mass of the polymerizable monomer may be, for example, 0.5 to 10 parts by mass, 1 to 8 parts by mass, or 2 to 6 parts by mass. Furthermore, the content of the styrene-based thermoplastic elastomer per 100 parts by mass of the monovinyl monomer may be, for example, 0.5 to 10 parts by mass, 1 to 8 parts by mass, or 2 to 6 parts by mass. Note that the styrene-based thermoplastic elastomer can be used alone or in combination of two or more types.

[0098] 1-3. Methods for Manufacturing Colored Resin Particles Generally, methods for manufacturing colored resin particles are broadly classified into dry methods such as pulverization methods, and wet methods such as emulsion polymerization agglutination methods, suspension polymerization methods, and dissolution suspension methods. Wet methods are preferred because they make it easier to obtain toner with excellent printing characteristics such as image reproducibility. Among wet methods, polymerization methods such as emulsion polymerization agglutination methods and suspension polymerization methods are preferred because they make it easier to obtain toner with a relatively small particle size distribution on the order of microns, and among polymerization methods, suspension polymerization methods are more preferred.

[0099] The emulsion polymerization agglutination method involves polymerizing an emulsified polymerizable monomer to obtain a resin fine particle emulsion, which is then agglutinated with a colorant dispersion or the like to produce colored resin particles. The dissolution suspension method involves dissolving or dispersing toner components such as binder resin and colorant in an organic solvent, forming droplets in an aqueous medium, and then removing the organic solvent to produce colored resin particles. Known methods can be used for both of these methods.

[0100] The colored resin particles used in this disclosure can be manufactured by a wet method or a dry method, and are not particularly limited, but among wet methods, a manufacturing method using suspension polymerization is preferred because it can produce colored resin particles with high average circularity, and is preferred from the viewpoint of improving image quality. The colored resin particles used in this disclosure can be manufactured, for example, by employing a preferred suspension polymerization method among wet methods, through the following process.

[0101] (A) Suspension polymerization As one embodiment of the method for producing colored resin particles using suspension polymerization, the following method can be cited: A method comprising: preparing a polymerizable monomer composition containing at least a polymerizable monomer, a colorant, and a charge control agent (preparation step of polymerizable monomer composition); preparing a suspension in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer (suspension step); and subjecting the suspension to a polymerization reaction (polymerization step).

[0102] The following describes each step of the above manufacturing method. In the manufacturing method described herein, two or more of the steps may be performed simultaneously as a single step, or they may be performed in a different order, as long as it is technically possible.

[0103] (A-1) Preparation process for polymerizable monomer composition First, a polymerizable monomer composition is prepared by mixing a polymerizable monomer, a colorant, a charge control agent, and, if necessary, other additives such as a softener, polar resin, styrene-based thermoplastic elastomer, and molecular weight adjuster. The material contained in the polymerizable monomer composition is the material of the core layer of the colored resin particles if it is a core-shell type colored resin particle, and the material of the colored resin particles if it is not a core-shell type colored resin particle. The polymerizable monomer, colorant, charge control agent, softener, polar resin, and styrene-based thermoplastic elastomer are as described above. The polymerizable monomer, which is the raw material for the binder resin, is used as the polymerizable monomer contained in the polymerizable monomer composition. For mixing when preparing the polymerizable monomer composition, for example, a media-type disperser is used. The content of polymerizable monomers is not particularly limited, but may be, for example, 60 to 95 parts by mass, 65 to 90 parts by mass, or 70 to 85 parts by mass per 100 parts by mass of the polymerizable monomer composition.

[0104] [Molecular Weight Adjuster] As other additives, it is preferable to use a molecular weight adjuster when polymerizing the polymerizable monomer that forms the binder resin. The molecular weight adjuster is not particularly limited as long as it is one that is generally used as a molecular weight adjuster for toner, and examples include mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, and 2,2,4,6,6-pentamethylheptan-4-thiol; thiuram disulfides such as tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, N,N'-dimethyl-N,N'-diphenyl thiuram disulfide, and N,N'-dioctadecyl-N,N'-diisopropyl thiuram disulfide; and so on. These molecular weight adjusters may be used individually or in combination of two or more. In this disclosure, the molecular weight adjusting agent is used in a ratio of typically 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, and more preferably 0.3 to 3 parts by mass, per 100 parts by mass of the polymerizable monomer (preferably a monovinyl monomer).

[0105] (A-2) Suspension process (droplet formation process) Next, a suspension is prepared in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer. For example, the suspension can be prepared by dispersing the polymerizable monomer composition in an aqueous medium containing a dispersion stabilizer, adding a polymerization initiator, and then forming droplets of the polymerizable monomer composition. The method of droplet formation is not particularly limited, but for example, it can be carried out using a device capable of strong stirring, such as an (in-line type) emulsifier / disperser (manufactured by Taiheiyo Kiko Co., Ltd., product name: Milder) or a high-speed emulsifier / disperser (manufactured by Primix Corporation, product name: T.K. Homomixer MARK II). In this disclosure, the aqueous medium containing the dispersion stabilizer may be referred to as the "aqueous dispersion medium".

[0106] Examples of polymerization initiators include persulfates such as potassium persulfate and ammonium persulfate; azo compounds such as 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide), 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobisisobutyronitrile; and organic peroxides such as di-t-butyl peroxide, benzoyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxydiethyl acetate, t-hexyl peroxy-2-ethylbutanoate, diisopropyl peroxydicarbonate, di-t-butyl peroxyisophthalate, and t-butyl peroxyisobutyrate. These can be used individually or in combination of two or more. Among these, organic peroxides are preferred because they reduce the amount of residual polymerizable monomers and the resulting positively charged toner exhibits excellent print durability. Among organic peroxides, peroxyesters are preferred because they have good initiator efficiency and reduce the amount of residual polymerizable monomers, and non-aromatic peroxyesters, i.e., peroxyesters without aromatic rings, are more preferred.

[0107] The polymerization initiator may be added after the polymerizable monomer composition has been dispersed in an aqueous medium and before droplet formation, as described above, or it may be added to the polymerizable monomer composition before it is dispersed in the aqueous medium.

[0108] In this disclosure, an aqueous medium refers to a medium whose main component is water. It is preferable to include a dispersion stabilizer in the aqueous medium. Examples of dispersion stabilizers include inorganic compounds such as sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, and ferric hydroxide; and organic compounds such as water-soluble polymers such as polyvinyl alcohol, methylcellulose, and gelatin; anionic surfactants; nonionic surfactants; and amphoteric surfactants. One or more of the above dispersion stabilizers can be used in combination.

[0109] Among the above-mentioned dispersion stabilizers, inorganic compounds, particularly colloids of poorly water-soluble metal hydroxides, are preferred. By using inorganic compounds, especially colloids of poorly water-soluble metal hydroxides, the particle size distribution of the colored resin particles can be narrowed, and the amount of residual dispersion stabilizer after washing can be reduced. As a result, the resulting positively charged toner can reproduce images clearly and has excellent environmental stability.

[0110] (A-3) Polymerization process After preparing a suspension by forming droplets of the polymerizable monomer composition in an aqueous medium as described in (A-2) above, the obtained suspension is subjected to a polymerization reaction. For example, the obtained suspension is heated to polymerize the polymerizable monomers in the suspension. This yields an aqueous dispersion of colored resin particles. The polymerizable monomers polymerize to form a binder resin. The polymerization temperature is preferably 50°C or higher, and more preferably 60 to 95°C. The polymerization reaction time is preferably 1 to 20 hours, and more preferably 2 to 15 hours.

[0111] The colored resin particles obtained by the polymerization process described above may be used as is as the colored resin particles contained in the positively charged toner of this disclosure. Alternatively, the colored resin particles obtained by the polymerization process described above may be used as a core layer, and a shell layer made of a different material on the outside thereof may be formed to obtain so-called core-shell type (or "capsule type") colored resin particles, which may then be used as the colored resin particles contained in the positively charged toner of this disclosure. The core-shell type colored resin particles can be used to balance lowering the fixing temperature and preventing aggregation during storage by coating a core layer made of a material having a lower softening point with a material having a higher softening point.

[0112] There are no particular restrictions on the method for producing core-shell type colored resin particles using the colored resin particles described above, and they can be produced by conventionally known methods. In situ polymerization and phase separation methods are preferred from the viewpoint of production efficiency.

[0113] The following describes a method for producing core-shell type colored resin particles by in situ polymerization. Core-shell type colored resin particles can be obtained by adding a polymerizable monomer for forming the shell layer (polymerizable monomer for the shell) and a polymerization initiator to an aqueous medium in which colored resin particles are dispersed, and then polymerizing them. In this case, the shell layer of the core-shell type colored resin particles consists of a polymer of the polymerizable monomer for the shell.

[0114] As the polymerizable monomer for the shell, the same polymerizable monomers as those described above can be used. Among these, monomers that yield polymers with a Tg of over 80°C, such as styrene, acrylonitrile, and methyl methacrylate, are preferably used individually or in combination of two or more. The amount of polymerizable monomer for the shell used is not particularly limited, but for example, it may be 0.1 to 10 parts by mass, 0.5 to 7 parts by mass, or 1 to 5 parts by mass per 100 parts by mass of the total amount of polymerizable monomer used to form the core layer. Furthermore, the content of polymerized polymerizable monomers for the shell in 100% by mass of the shell layer may be, for example, 90% by mass or more, 95% by mass or more, or 99% by mass or more, and the shell layer may consist only of polymerized polymerized monomers for the shell.

[0115] Examples of polymerization initiators used for polymerizing polymerizable monomers for shells include metal persulfate salts such as potassium persulfate and ammonium persulfate; azo-based initiators such as 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide) and 2,2'-azobis-(2-methyl-N-(1,1-bis(hydroxymethyl)2-hydroxyethyl)propionamide); and other water-soluble polymerization initiators. These can be used individually or in combination of two or more. The amount of polymerization initiator is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of polymerizable monomer for shells.

[0116] The polymerization temperature of the shell layer is preferably 50°C or higher, and more preferably 60 to 95°C. The polymerization reaction time is preferably 1 to 20 hours, and more preferably 2 to 15 hours.

[0117] (A-4) Washing, filtration, dehydration, and drying process In the above manufacturing method, after polymerization is complete, the aqueous dispersion of colored resin particles is preferably washed, filtered, dehydrated, and dried several times as needed, in accordance with conventional methods to remove the dispersion stabilizer.

[0118] Regarding the above cleaning method, when an inorganic compound is used as a dispersion stabilizer, it is preferable to dissolve and remove the dispersion stabilizer in water by adding an acid or alkali to the aqueous dispersion of colored resin particles. When a colloid of a poorly water-soluble metal hydroxide is used as a dispersion stabilizer, it is preferable to add an acid to adjust the pH of the aqueous dispersion of colored resin particles to 6.5 or less. As the acid to be added, inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, as well as organic acids such as formic acid and acetic acid, can be used, but sulfuric acid is particularly preferred due to its high removal efficiency and low burden on manufacturing equipment.

[0119] The dehydration and filtration methods are not particularly limited and can be any of the known methods. For example, centrifugal filtration, vacuum filtration, and pressure filtration can be used. Similarly, the drying method is not particularly limited and can be any of the various methods used.

[0120] (B) Grinding Method When colored resin particles are produced using the grinding method, the process is as follows: First, a binder resin, a colorant, a static charge control agent, and, if necessary, other additives such as a softener, polar resin, and styrene-based thermoplastic elastomer are mixed using a mixer, such as a ball mill, V-type mixer, FM mixer (trade name, manufactured by Nippon Coke Industries Co., Ltd.), high-speed dissolver, or internal mixer. The binder resin, colorant, static charge control agent, softener, polar resin, and styrene-based thermoplastic elastomer are as described above. Next, the mixture obtained above is kneaded while heating using a pressure kneader, twin-screw extruder, roller, etc. The resulting kneaded material is coarsely ground using a grinder such as a hammer mill, cutter mill, or roller mill. After further fine grinding using a grinder such as a jet mill or high-speed rotary grinder, the material is classified to the desired particle size using a classifier such as an air-powered classifier or pneumatic classifier to obtain colored resin particles by the grinding method. The colored resin particles obtained by the pulverization method can also be converted into core-shell type colored resin particles by methods such as in situ polymerization, similar to the colored resin particles obtained by the suspension polymerization method (A) described above.

[0121] 1-4. Toner Properties The positively charged toner of this disclosure is an aggregate of toner particles. These toner particles may be particles in which the above-mentioned external additive has been added to the surface of the above-mentioned colored resin particles.

[0122] The volume-average particle size (Dv) of the positively charged toner of this disclosure is not particularly limited, but is preferably 5.5 to 9.5 μm, and more preferably 6.5 to 8.5 μm. When Dv is above the lower limit, the fluidity of the toner can be improved, toner ejection can be suppressed, and deterioration of transferability and decrease in image density can be suppressed. When Dv is below the upper limit, deterioration of toner fixation can be suppressed, and a decrease in image resolution can be suppressed. Since the volume-average particle size of the toner is not affected by the presence or absence of external additives, the volume-average particle size of the colored resin particles can be considered as the volume-average particle size of the toner.

[0123] In this disclosure, the volume-average particle size and number-average particle size can be measured, for example, using a particle size distribution analyzer that employs the Coulter counter method (e.g., Beckman Coulter, product name: Multisizer). A dispersion of the particles to be measured is used as the sample for measurement. For example, 0.2 g of the particles to be measured is placed in a beaker, an aqueous surfactant solution (e.g., Fujifilm's "Drywell") is added as a dispersant, then 2 ml of a dispersion medium (e.g., Beckman Coulter's "Isoton II") is added to wet the particles, then 10 ml of the dispersion medium is added, and the particles are dispersed in an ultrasonic disperser for 1 minute before measurement is performed using a particle size distribution analyzer (e.g., Beckman Coulter's "Multisizer"). The aperture diameter during this measurement may be, for example, 100 μm. The volume-average particle size is the 50% cumulative diameter in the particle size distribution determined by volume, and the number-average particle size is the 50% cumulative diameter in the particle size distribution determined by number.

[0124] The average circularity of the positively charged toner of this disclosure is not particularly limited, but from the viewpoint of transferability and fine line reproducibility, it is preferably 0.95 to 1.00, more preferably 0.97 to 1.00, and even more preferably 0.98 to 1.00. Circularity is defined as the value obtained by dividing the perimeter of a circle having the same projection area as the particle image by the perimeter of the projected image of the particle. The average circularity in this disclosure is used as a simple method to quantitatively express the shape of the particle and is an index that indicates the degree of unevenness of the toner particle. The average circularity is 1 when the toner particle is a perfect sphere, and becomes a smaller value as the surface shape of the toner particle becomes more complex. The above circularity and average circularity can be measured using the Sysmex Corporation flow-type particle image analyzer "FPIA-3000".

[0125] The blow-off charge of the positively charged toner of this disclosure is not particularly limited, but may be, for example, 8 to 40 μC / g or 10 to 20 μC / g, in order to have sufficient positive charge properties. The blow-off charge of the toner is measured by the blow-off charge measurement method described in the examples below.

[0126] The present disclosure will be further described below with reference to examples and comparative examples, but the present disclosure is not limited to these examples. Parts and percentages are by mass unless otherwise specified.

[0127] The weight-average molecular weight (Mw) of the polymer was measured by GPC and determined in polystyrene equivalent. For the measurement sample, the polymer was dissolved in tetrahydrofuran (THF) to a concentration of 2 mg / mL, sonicated for 10 minutes, and then passed through a 0.45 μm membrane filter. The measurement conditions were: temperature: 40°C, solvent: tetrahydrofuran, flow rate: 1.0 mL / min, concentration: 0.2 wt%, sample injection volume: 100 μL. The column used was a GPC TSKgel MultiporeHXL-M (30 cm x 2) manufactured by Tosoh Corporation. Furthermore, measurements were performed under conditions where the linear correlation equation between Log(Mw) and elution time for weight-average molecular weights (Mw) between 1,000 and 300,000 was 0.98 or higher.

[0128] [SrTiO ３Preparation of particles A to J: Metatitanic acid and the TiO of metatitanic acid ２ A solution of strontium chloride in an amount having a molar ratio of 1.15 to strontium chloride, and a solution of lanthanum chloride in an amount of lanthanum shown in Table 1 relative to the Sr of strontium chloride, were added to a reaction vessel to obtain a slurry. The obtained slurry was heated to 90°C while stirring, and then a 10N sodium hydroxide aqueous solution was gradually added. Stirring continued at 95°C for 1 hour, and the slurry was cooled to 50°C to terminate the reaction. Next, hydrochloric acid was added to the slurry and stirring continued until a precipitate formed, at which point decantation washing was performed. Hydrochloric acid was added to the precipitate after washing, and a surface treatment agent was added in the amount shown in Table 1 per 100 parts by mass of the solid content of the precipitate, and the mixture was stirred at 70°C. Next, the precipitate was filtered, washed, and dried to obtain SrTiO ３ Particles A to J were obtained. The obtained SrTiO ３ For particles A to J, along with the amount of surface treatment agent added, the SrTiO after surface treatment. ３ Table 1 shows the coating amount (mass%) of the surface treatment agent when the particle mass is set to 100% by mass. The coating amount was calculated from the amount of surface treatment agent added, the adhesion rate of the surface treatment agent, and the mass of the strontium titanate particles obtained after surface treatment. The adhesion rate of the surface treatment agent was determined by analyzing the carbon content of the strontium titanate particles after surface treatment using a carbon-sulfur analyzer and dividing the measured value by the carbon content when the theoretical amount of surface treatment agent is applied. The specific formula for calculating the coating amount of the surface treatment agent was as follows: Coating amount (mass%) of surface treatment agent = 100 × {(amount of surface treatment agent added) × (adhesion rate of surface treatment agent)} / (mass of strontium titanate particles after surface treatment)

[0129]

[0130] SrTiO ３ The number-average primary particle size of particles A to J was in the range of 30 to 40 nm.

[0131] [Production Example 1: Production of Polar Resin P1] 200 parts of toluene were added to the reaction vessel, and the reaction vessel was thoroughly replaced with nitrogen while stirring the toluene, and then the temperature was raised to 90°C. Subsequently, a mixed solution of 97.0 parts of methyl methacrylate, 2.6 parts of ethyl acrylate, 0.4 parts of acrylic acid, and 3 parts of t-butyl peroxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl® O) was added dropwise to the reaction vessel over 2 hours. Furthermore, polymerization was completed by holding under reflux of toluene for 10 hours, and then the solvent was removed by distillation under reduced pressure. Polar resin P1 (MMA / EA / AA) was obtained in this manner. The obtained polar resin P1 had an acid value of 2.5 mg KOH / g, a Tg of 74°C, and a Mw of 12600.

[0132] [Production Example 2: Synthesis of SIS Composition] 23.2 kg of cyclohexane, 1.5 mmol of N,N,N',N'-tetramethylethylenediamine, and 1.70 kg of styrene were added to a pressure reactor and stirred at 40°C. 99.1 mmol of n-butyllithium was then added, and the resulting mixture was polymerized for 1 hour while increasing the temperature to 50°C. The polymerization conversion rate of styrene was 100% by weight. Subsequently, 6.03 kg of isoprene was continuously added to the reactor over 1 hour while maintaining a temperature of 50-60°C. After the addition of isoprene was completed, polymerization was carried out for another hour to obtain styrene-isoprene triblock copolymer (a). The polymerization conversion rate of isoprene was 100%. Next, 15.0 mmol of dimethyldichlorosilane was added as a coupling agent, and a coupling reaction was carried out for 2 hours to obtain styrene-isoprene-styrene triblock copolymer (b). Subsequently, 198 mmol of methanol was added as a polymerization inhibitor and thoroughly mixed to stop the reaction, thereby obtaining a reaction solution containing a styrene-isoprene-styrene triblock copolymer (SIS) composition containing the block copolymers (a) and (b). Then, 0.3 parts of 2,6-di-tert-butyl-p-cresol was added to 100 parts of the reaction solution thus obtained (containing 30 parts of the polymer component) as an antioxidant and mixed. The mixed solution was then added dropwise in small amounts to warm water heated to 85-95°C to evaporate the solvent and obtain a precipitate. This precipitate was pulverized and dried with hot air at 85°C to recover the SIS composition.

[0133] [Production Example 3: Production of Colored Resin Particles 1] 1. Preparation of Polymerizable Monomer Composition for Core: 72 parts of styrene (ST), 28 parts of n-butyl acrylate (BA), 9 parts of carbon black (Mitsubishi Chemical Corporation, trade name: #25B) as a coloring agent, and 1.0 part of polar resin P1 obtained in Production Example 1 were mixed and dispersed using a media-type emulsifier / disperser (trade name: Dynomil, Shinmaru Enterprises) to obtain a polymerizable monomer mixture. To the obtained mixture, 0.5 parts of divinylbenzene, 1.0 part of tetraethyl thiuram disulfide as a molecular weight modifier, 1.5 parts of CCR-A1 (copolymerization ratio of quaternary ammonium salt-containing monomer: 2.0%) which is a positively charged charge control resin, 1.0 part of CCR-B1 (copolymerization ratio of quaternary ammonium salt-containing monomer: 1.0%) which is a positively charged charge control resin, and behenyl stearate (molecular formula: C) as a softener. １７ H ３５ -COO-C ２２ H ４５ 20 parts of a SIS composition obtained in the above production example 2, with a melting point of 67.1°C, an acid value of 0.1 mg KOH / g, a hydroxyl value of 0.3 mg KOH / g, and an esterification rate of 98%, were added and mixed to obtain a polymerizable monomer composition for the core.

[0134] 2. Preparation of aqueous dispersion medium: On the other hand, in a stirred tank, at room temperature, an aqueous solution prepared by dissolving 7.4 parts magnesium chloride in 250 parts deionized water was gradually added under stirring to an aqueous solution prepared by dissolving 4.1 parts sodium hydroxide in 50 parts deionized water to prepare a magnesium hydroxide colloidal dispersion (3.0 parts magnesium hydroxide).

[0135] 3. Droplet Formation Process: The polymerizable monomer composition for the core was added to the magnesium hydroxide colloidal dispersion obtained above at room temperature and stirred until the droplets stabilized. Then, 3.5 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl® O) were added as a polymerization initiator, and the mixture was stirred at a rotational speed of 15,000 rpm using an in-line emulsifying disperser (manufactured by Taiheiyo Kiko Co., Ltd., trade name: Milder) to form droplets of the polymerizable monomer composition for the core.

[0136] 4. Polymerization process: A suspension containing droplets of the polymerizable monomer composition for the core obtained above was placed in a reactor equipped with a stirring blade, and the temperature was raised to 90°C to start the polymerization reaction. When the polymerization conversion rate reached approximately 100%, 3.0 parts of methyl methacrylate were added to the reactor as a polymerizable monomer for the shell. The polymerization was then continued for another 3 hours at 90°C, after which the reaction was stopped by water cooling to obtain an aqueous dispersion of core-shell type colored resin particles.

[0137] 5. Washing, Filtration, Dehydration, and Drying Process: The aqueous dispersion of colored resin particles obtained above was acid washed at room temperature by adding sulfuric acid dropwise while stirring until the pH was 5.5 or lower. Next, filtration separation was performed, and 500 parts of deionized water were added to the obtained solid to form a slurry again, and the water washing treatment (washing, filtration, and dehydration) was repeated several times. Next, filtration separation was performed, and the obtained solid was placed in the container of a dryer and dried at 40°C for 24 hours to obtain dried colored resin particles 1. The volume-average particle size of the obtained colored resin particles 1 was 7.9 μm.

[0138] [Example 1] To the colored resin particles 1 (100 parts by mass) obtained in Production Example 3 above, 0.80 parts of hydrophobized silica particles (manufactured by Wacker, product name: H05TA) with a number average primary particle size of 50 nm as silica particle A, 0.56 parts of hydrophobized silica particles (manufactured by Cabot, product name: TG-7120) with a number average primary particle size of 20 nm as silica particle B, 0.20 parts of hydrophobized silica particles (manufactured by Cabot, product name: TG-820F) with a number average primary particle size of 7 nm as silica particle C, 0.1 parts of fatty acid metal salt particles (zinc stearate particles, manufactured by Sakai Chemical Industry Co., Ltd., product name: SPZ-100F) with a number average primary particle size of 0.5 μm as metal soap fine particles D, and the above SrTiO ３ Positively charged toner of Example 1 was prepared by adding 0.93 parts of particle A and mixing and stirring using a high-speed agitator (manufactured by Nippon Coke Industries Co., Ltd., product name: FM Mixer) under the conditions of a blade peripheral speed of 46.6 m / s and an external additive treatment time of 10 minutes.

[0139] [Examples 2-8 and Comparative Examples 1-4] Positively charged toners for Examples 2-8 and Comparative Examples 1-4 were obtained in the same manner as in Example 1, except that the external additives added were changed according to Table 2.

[0140] [Evaluation] 1. Toner ejection after being left in high temperature and high humidity (HH) conditions Toner was filled into a printer cartridge (Brother Industries, Ltd., HL-L9310CDW) and left for 24 hours under high temperature and high humidity (HH) conditions of 35°C and 80% humidity. Using a pre-made jig that allows the cartridge to spin freely, the cartridge was run at 150 revolutions per minute, and the weight of toner ejected from the cartridge in 15 seconds was measured. The less toner ejected from the cartridge, the less likely to toner is to be ejected in a high temperature and high humidity environment. The likelihood of toner ejection in a high temperature and high humidity environment was evaluated according to the following evaluation criteria. <Evaluation Criteria> A: Toner ejected weight is less than 10 mg B: Toner ejected weight is 10 mg or more and less than 25 mg C: Toner ejected weight is 25 mg or more and less than 40 mg D: Toner ejected weight is 40 mg or more

[0141] 2. High Temperature and High Humidity (HH) Initial Fogging Test In the evaluation of toner ejection after being left in the high temperature and high humidity (HH) environment described above, the cartridge was run idly until toner ejection stopped. Then, the cartridge was set in a commercially available non-magnetic single-component developing printer (printing speed: 31 pages / minute), and three consecutive prints were made at a 5% print density under a high temperature and high humidity (H / H) environment of 35°C and 80% RH. After that, solid white printing (print density 0%) was performed, and the solid white printing was stopped midway. The toner from the non-image area on the photoreceptor after development was then attached to adhesive tape (Sumitomo 3M Co., Ltd., product name: Scotch Mending Tape 810-3-18). This was then attached to a new sheet of paper. Next, the whiteness (B) of the printing paper with the adhesive tape attached was measured using a whiteness meter (manufactured by Nippon Denshoku Co., Ltd.). Similarly, only unused adhesive tape was attached to the printing paper, and its whiteness (A) was measured. The difference in whiteness (B - A) was defined as the fogging value. A smaller fogging value indicates less fogging and better print quality. The likelihood of fogging occurring in the initial stages of printing in a high-temperature, high-humidity environment was evaluated according to the following evaluation criteria: <Evaluation Criteria> A: Fogging value less than 0.5 B: Fogging value 0.5 or more and less than 1 C: Fogging value 1 or more and less than 2 D: Fogging value 2 or more

[0142] 3. Solid Color Tracking Performance Print paper was loaded into a commercially available non-magnetic single-component developing printer (printing speed: 31 pages / minute), toner was added to the developing unit, and the printer was left for 24 hours in a normal temperature and humidity (NN) environment at 23°C and 50% RH. Then, continuous printing was performed from the beginning at a print density of 5% under the same conditions. On the 10th print, solid black printing (print density 100%) was performed, and the image density at the leading edge (50 mm from the leading edge) and the image density at the trailing edge (50 mm from the trailing edge) were measured using a reflective image densitometer (product name: RD918, manufactured by Macbeth Corporation), and the difference in image density between the leading and trailing edges (ΔD) was calculated. The smaller the ΔD, the better the solid color tracking performance can be evaluated. Solid color tracking performance in a normal temperature and humidity environment was evaluated according to the following evaluation criteria. <Evaluation Criteria> A: ΔD is less than 0.1 B: ΔD is 0.1 or more and less than 0.2 C: ΔD is 0.2 or more and less than 0.3 D: ΔD is 0.3 or more and less than 0.4 E: ΔD is 0.4 or more

[0143] 4. Toner Blow-Off Charge Amount 0.25 g of toner and 9.75 g of a standard carrier, ferrite carrier (product name: EF-60, manufactured by Powdertec, Mn-Mg-Sr-Fe system, spherical, no resin coating, average particle size 60 μm), were placed in a glass container with a volume of 30 cc (internal dimensions: bottom diameter 30 mm, height 50 mm). Triboelectric charging treatment was performed using a roller-type agitator, rotating at 160 revolutions / minute for 30 minutes in an environment of 23°C and relative humidity 50%. 1.2 g of the mixture of toner and ferrite carrier after the triboelectric treatment was placed in a Faraday cage. Using a blow-off powder charge measuring device (product name: Q / M meter, manufactured by Epping), a mesh with a mesh opening of 16 μm was attached to the cell, and the mixture was blown off for 90 seconds under conditions of a suction pressure of 1.05 mbar and a nitrogen gas flow rate of 2.0 L / min to measure the blow-off charge amount (μC) of the mixture. The blow-off charge amount (μC / g) of the toner was calculated using the following formula (1): Formula (1) Blow-off charge amount of toner (μC / g) = Blow-off charge amount of mixture (μC) / Amount of toner blown off during measurement (g)

[0144]

[0145] The positively charged toners of Examples 1 to 8 contained strontium titanate particles as an external additive, which were doped with metal elements other than titanium and strontium and surface-treated with fatty acid alkali metal salts. As a result, they possessed sufficient positive charge, excellent solid-coverage tracking, and were less prone to fogging and toner ejection in high-temperature, high-humidity environments. On the other hand, the positively charged toners of Comparative Examples 1 and 2 contained strontium titanate particles as an external additive, which were treated with organosilicon compounds instead of fatty acid alkali metal salts as a surface treatment agent. The positively charged toner of Comparative Example 3 used fatty acid alkali metal salts as a surface treatment agent, but contained strontium titanate particles as an external additive that were not doped with metal elements other than titanium and strontium. The positively charged toner of Comparative Example 4 contained untreated strontium titanate particles as an external additive. These comparative examples of positively charged toners had low charge levels, poor solid-coverage tracking, and were prone to fogging and toner ejection in high-temperature, high-humidity environments.

Claims

1. A positively charged toner comprising colored resin particles and an external additive containing strontium titanate particles, wherein the strontium titanate particles are doped with metal elements other than titanium and strontium, and at least a portion of the particle surface is coated with an alkali metal fatty acid salt.

2. The positively charged toner according to claim 1, wherein the colored resin particles contain a quaternary ammonium salt-containing copolymer as a positively charged charge control agent.

3. The positively charged toner according to claim 1 or 2, wherein the metal element doped into the strontium titanate particles is lanthanum.

4. The positively charged toner according to claim 1 or 2, wherein the coating amount of the fatty acid alkali metal salt is 4% by mass or more and 20% by mass or less with respect to 100% by mass of the strontium titanate particles.

5. The positively charged toner according to claim 1 or 2, wherein the external additive further comprises an external additive different from the strontium titanate particles.

6. The positively charged toner according to claim 1 or 2, wherein the external additive further contains silica particles, and the ratio of the silica particle content to the strontium titanate particle content is 0.5 to 10.0.

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