Two-component developer

Abstract

With respect to a two-component developer according to the present invention, external additive particles in toner particles contain silica particles. The number average primary particle diameter of the silica particles is 30 nm to 120 nm. A coat layer of each carrier particle contains a coat resin and barium titanate particles. The coat resin contains a silicone resin. The number average primary particle diameter of the barium titanate particles is 100 nm to 500 nm. The content of the barium titanate particles is 5 parts by mass to 45 parts by mass relative to 100 parts by mass of the coat resin. The ratio of the mass of the coat layer to the mass of the carrier core is 0.09% by mass to 4.90% by mass. The coverage of the carrier core is not less than 80.0% but less than 100.0%.

Description

Technical Field

[0001] The present invention relates to a two-component developer.

Background Art

[0002] In an image forming apparatus that forms an image using toner, in order to stably form an image with a desired image density, it is required to stably charge the toner to a desired charge amount. In order to suppress the charge-up of the toner, for example, the positively charged cyan developer described in Patent Document 1 includes toner and a carrier. The carrier has core particles and a resin coat provided on the surface of the core particles. The resin coat coverage rate on the surface of the core particles is 60% to 90%.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the positively charged cyan developer described in Patent Document 1 has room for improvement in terms of anti-fogging properties, stably forming an image with a desired image density, suppressing the occurrence of carrier development, and suppressing the occurrence of image defects caused by poor cleaning.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a two-component developer that is excellent in anti-fogging properties, can stably form an image with a desired image density, can suppress the occurrence of carrier development, and is less likely to cause image defects due to poor cleaning.

Means for Solving the Problems

[0006] The two-component developer according to the present invention includes toner containing toner particles and a carrier containing carrier particles. The toner particles have toner mother particles and external additive particles provided on the surface of the toner mother particles. The external additive particles include silica particles. The number average primary particle diameter of the silica particles is 30 nm or more and 120 nm or less. The carrier particles have a carrier core and a coat layer covering the surface of the carrier core. The coat layer includes a coat resin and barium titanate particles. The coat resin includes a silicone resin. The number average primary particle diameter of the barium titanate particles is 100 nm or more and 500 nm or less. The content of the barium titanate particles is 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coat resin. The ratio of the mass of the coat layer to the mass of the carrier core is 0.09% by mass or more and 4.90% by mass or less. The coverage rate of the carrier core is 80.0% or more and less than 100.0%. The coverage rate is the ratio of the area of the coated region covered by the coat layer to the area of the surface of the carrier core.

Advantages of the Invention

[0007] According to the two-component developer of the present invention, it has excellent anti-fogging properties, can stably form an image with a desired image density, can suppress the occurrence of carrier development, and is less likely to cause image defects due to poor cleaning.

Brief Description of the Drawings

[0008]

Figure 1

Modes for Carrying Out the Invention

[0009] First, the meanings of the terms used in this specification and the measurement methods will be explained. A toner is an aggregate of toner particles (for example, a powder). An external additive is an aggregate of external additive particles (for example, a powder). A carrier is an aggregate of carrier particles (for example, a powder). The evaluation results (values indicating shape, physical properties, etc.) regarding powders (more specifically, powders of toner particles, powders of external additive particles, powders of carrier particles, etc.) are the arithmetic means of the values measured for each of a considerable number of particles of the powder, unless otherwise specified. The "main component" of a material means the component most contained in the material on a mass basis, unless otherwise specified. The strength of hydrophobicity (or hydrophilicity) can be represented, for example, by the contact angle of a water droplet (ease of wetting by water). The larger the contact angle of the water droplet, the stronger the hydrophobicity. In some cases, a "system" may be appended after a compound name to comprehensively denote the compound and its derivatives. When a "system" is appended after a compound name to represent a polymer name, it means that the repeating unit of the polymer is derived from the compound or its derivative. Each component described in this specification may be used alone or in combination of two or more kinds.

[0010] Volume median diameter (D 50Unless otherwise specified, it is the median diameter measured on a volume basis using a laser diffraction / scattering particle size distribution analyzer ("LA-950" manufactured by Horiba, Ltd.). The number-average primary particle diameter is the number-average value of the equivalent circle diameters (Heywood diameters: the diameters of circles having the same area as the projected area of the primary particles) of the primary particles measured using a scanning electron microscope, unless otherwise specified. The number-average primary particle diameter is, for example, the number-average value of the equivalent circle diameters of 100 primary particles. The softening point (Tm) is the value measured using a thermomechanical analyzer ("CFT-500D" manufactured by Shimadzu Corporation), unless otherwise specified. In the S-shaped curve measured by the thermomechanical analyzer (horizontal axis: temperature, vertical axis: stroke), the temperature at which "(baseline stroke value + maximum stroke value) / 2" is the softening point. The melting point (Mp) is the temperature of the maximum endothermic peak in the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured using a differential scanning calorimeter ("DSC-6220" manufactured by Seiko Instruments Inc.), unless otherwise specified. This endothermic peak appears due to the melting of the crystallization sites. The glass transition point (Tg) is the value measured in accordance with "JIS (Japanese Industrial Standards) K7121-2012" using a differential scanning calorimeter ("DSC-6220" manufactured by Seiko Instruments Inc.), unless otherwise specified. In the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured by the differential scanning calorimeter, the temperature of the inflection point due to the glass transition (specifically, the temperature of the intersection of the extrapolated line of the baseline and the extrapolated line of the descending line) corresponds to the glass transition point. Each of the acid value and the hydroxyl value is the value measured in accordance with "JIS (Japanese Industrial Standards) K0070-1992", unless otherwise specified. Each of the weight-average molecular weights (Mw) is the value measured using gel permeation chromatography, unless otherwise specified. The charge amount (unit: μC / g) is the value measured using an aspirating small charge amount measuring device ("MODEL 212HS" manufactured by Trek) in an environment at a temperature of 25°C and a relative humidity of 50%RH, unless otherwise specified. The strength of the chargeability is the ease of triboelectric charging with respect to a standard carrier provided by the Japan Society for Imaging Science, unless otherwise specified.For example, by stirring a standard carrier (anionic: N-01, cationic: P-01) provided by the Japan Society for Imaging Science and Technology and the object to be measured, the object to be measured is triboelectrically charged. For example, using a Q / m meter ("MODEL 212HS" manufactured by Trek), the charge amount per unit mass of the object to be measured before and after triboelectric charging is measured respectively. It shows that the greater the change in the charge amount per unit mass before and after triboelectric charging of the object to be measured, the stronger the chargeability. Above, the meaning of the terms used in this specification and the measurement method have been described.

[0011] [Two-component developer] Hereinafter, with reference to FIG. 1, a two-component developer (hereinafter, may be referred to as a developer) 1 according to an embodiment of the present invention will be described. FIG. 1 shows the developer 1 according to this embodiment. In FIG. 1, a plurality of identical elements are indicated by the same hatching, one of these identical elements is labeled, and the remaining labels of these identical elements are omitted.

[0012] The developer 1 includes toner and a carrier. The toner includes toner particles 10. The carrier includes carrier particles 20. The toner particles 10 have a toner mother particle 11 and external additive particles 12. The external additive particles 12 are provided on the surface of the toner mother particle 11. The external additive particles 12 include silica particles 13. The number average primary particle diameter of the silica particles 13 is 30 nm or more and 120 nm or less. The carrier particles 20 have a carrier core 21 and a coating layer 22. The coating layer 22 covers the surface of the carrier core 21. The coating layer 22 includes a coating resin and barium titanate particles 23. The coating resin includes a silicone resin. The number average primary particle diameter of the barium titanate particles 23 is 100 nm or more and 500 nm or less. The content of the barium titanate particles 23 is 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coating resin. The ratio of the mass of the coating layer 22 to the mass of the carrier core 21 is 0.09% by mass or more and 4.90% by mass or less. The coverage rate of the carrier core 21 is 80.0% or more and less than 100.0%. This coverage rate of the carrier core 21 is the ratio of the area of the coated region A1 covered by the coating layer 22 to the area of the surface of the carrier core 21.

[0013] Hereinafter, the "ratio of the mass of the coating layer 22 to the mass of the carrier core 21" may be referred to as the "coating layer / core ratio". Further, the "silica particles 13 having a number average primary particle diameter of 30 nm or more and 120 nm or less" may be referred to as the "large-diameter silica particles 13".

[0014] By having the above configuration, the developer 1 according to the present embodiment is excellent in anti-fogging property, can stably form an image with a desired image density, can suppress the occurrence of carrier development, and is less likely to cause image defects due to poor cleaning. The reason is presumed as follows.

[0015] In the developer 1 according to the present embodiment, the coating layer 22 of the carrier particles 20 contains barium titanate particles 23. Since the barium titanate particles 23, which are ferroelectrics, have a high relative permittivity, the charge retention ability of the carrier particles 20 containing the barium titanate particles 23 in the coating layer 22 is high. The carrier particles 20 with high charge retention ability can impart a sufficient amount of charge to the toner particles 10 by contact with the toner particles 10. Here, when printing a large number of images using an image forming apparatus, the toner concentration in the developer 1 accommodated in the developing apparatus may vary during printing. However, the carrier particles 20 with high charge retention ability can impart a sufficient amount of charge to the toner particles 10 up to the saturation charge amount of the toner particles 10 even when the toner concentration in the developer 1 increases and the number of toner particles 10 to be charged increases. As a result, even when the toner concentration in the developer 1 changes, the variation in the charge amount of the toner can be reduced, and an image with a desired image density can be stably formed. Further, since the carrier particles 20 can impart a sufficient amount of charge to the toner particles 10, the toner particles 10 with a charge amount less than the desired value and the reversely charged toner particles 10 can be reduced, and an image with less fogging can be formed.

[0016] In the developer 1 according to this embodiment, the number average primary particle diameter of the barium titanate particles 23 is 100 nm or more and 500 nm or less. When the number average primary particle diameter of the barium titanate particles 23 is less than 100 nm, the relative permittivity thereof tends to decrease. Since the number average primary particle diameter of the barium titanate particles 23 is 100 nm or more, the relative permittivity of the barium titanate particles 23 becomes sufficiently high. By having the coating layer 22 containing the barium titanate particles 23 with a high relative permittivity, the carrier particles 20 can impart a sufficient amount of charge to the toner particles 10. Therefore, even when the toner concentration in the developer 1 changes, fluctuations in the charge amount of the toner can be reduced, and an image with a desired image density can be stably formed. Further, since the carrier particles 20 can impart a sufficient amount of charge to the toner particles 10, the toner particles 10 having a charge amount less than the desired value and the toner particles 10 charged reversely can be reduced, and an image with less fogging can be formed. On the other hand, when the number average primary particle diameter of the barium titanate particles 23 is 500 nm or less, the barium titanate particles 23 are incorporated into the coating layer 22 and are difficult to desorb from the coating layer 22. Therefore, it is possible to suppress the barium titanate particles 23 from desorbing and being carried to the gap between the photoreceptor drum and the cleaning blade. As a result, cleaning failure, and thus image failure caused by this, are less likely to occur.

[0017] In the developer 1 according to this embodiment, the content of the barium titanate particles 23 is 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coating resin. When the content of the barium titanate particles 23 is 5 parts by mass or more with respect to 100 parts by mass of the coating resin, the amount of the barium titanate particles 23 in the coating layer 22 increases, and the charge holding ability of the carrier particles 20 is enhanced. The carrier particles 20 having a high charge holding ability can impart a sufficient amount of charge to the toner particles 10 by contact with the toner particles 10. Therefore, even when the toner concentration in the developer 1 changes, fluctuations in the charge amount of the toner can be reduced, and an image with a desired image density can be stably formed. Further, since the carrier particles 20 can impart a sufficient amount of charge to the toner particles 10, the amount of toner particles 10 having a charge amount less than the desired value and reversely charged toner particles 10 can be reduced, and an image with less fogging can be formed. On the other hand, when the content of the barium titanate particles 23 is 45 parts by mass or less with respect to 100 parts by mass of the coating resin, the barium titanate particles 23 are incorporated into the coating layer 22 and are difficult to desorb from the coating layer 22. Therefore, the contact between the toner particles 10 and the carrier particles 20 is less likely to be inhibited by the desorbed barium titanate particles 23. Therefore, a sufficient amount of charge can be imparted from the carrier particles 20 to the toner particles 10. As a result, the amount of toner particles 10 having a charge amount less than the desired value and reversely charged toner particles 10 can be reduced, and an image with less fogging can be formed.

[0018] In the developer 1 according to this embodiment, the coat layer / core rate of the carrier particles 20 is 0.09 mass% or more and 4.90 mass% or less. When the coat layer / core rate is 4.90 mass% or less, the coat layer 22 becomes appropriately thin. The coat resin contained in the coat layer 22 has hygroscopicity. When the coat layer 22 becomes appropriately thin, the amount of the coat resin decreases, and the influence on triboelectrification caused by the hygroscopic coat resin (for example, the influence that the triboelectrification amount of the toner particles 10 decreases) can be reduced. Further, when the coat layer / core rate is 4.90 mass% or less, aggregation of the carrier particles 20 with each other can be suppressed when forming the coat layer 22 in the carrier formation process described later. Since the non-aggregated or less-aggregated carrier particles 20 are preferably triboelectrified, the toner particles 10 are triboelectrified to a desired electrification amount. As a result, the toner particles 10 having an electrification amount less than the desired value and the reversely electrified toner particles 10 can be reduced, and an image with less fogging can be formed. On the other hand, when the coat layer / core rate is 0.09 mass% or more, the coat layer 22 does not become too thin. As a result, due to the contact between the coat layer 22 of the carrier particles 20 and the toner particles 10, the toner particles 10 are triboelectrified to a desired electrification amount. And the toner particles 10 having an electrification amount less than the desired value and the reversely electrified toner particles 10 can be reduced, and an image with less fogging can be formed. Further, when the coat layer / core rate is 0.09 mass% or more, the occurrence of a defect (carrier development) in which the carrier particles 20 adhere to the photosensitive drum is suppressed.

[0019] In the developer 1 according to the present embodiment, the coverage rate of the carrier core 21 is 80.0% or more and less than 100.0%. Since the coverage rate of the carrier core 21 is less than 100.0% and not 100.0%, the coat layer 22 does not completely cover the entire surface of the carrier core 21. The coat layer 22 partially covers the surface of the carrier core 21. As shown in FIG. 1, the carrier core 21 has a coated region A1 and an uncoated region A2. The coated region A1 is a region of the surface of the carrier core 21 that is covered by the coat layer 22. The uncoated region A2 is a region of the surface of the carrier core 21 that is not covered by the coat layer 22. In the uncoated region A2, the carrier core 21 is exposed without being covered by the coat layer 22.

[0020] Since the coverage rate of the carrier core 21 is less than 100.0% and not 100.0%, there is an uncoated region A2 on the carrier core 21 that is not covered by the coat layer 22. The coat resin contained in the coat layer 22 has hygroscopicity. The presence of the uncoated region A2 can reduce the influence on triboelectrification caused by the hygroscopic coat resin (for example, the influence that the triboelectrification amount of the toner particles 10 decreases). Further, since it is not covered by the coat layer 22 containing the coat resin, the electrical resistance of the uncoated region A2 is low, and charges easily move in the uncoated region A2. The presence of the uncoated region A2 where charges easily move allows the toner particles 10 to be triboelectrically charged to a desired charge amount in a short time by contact with the carrier particles 20. Further, the presence of the uncoated region A2 where charges easily move prevents the toner particles 10 from being over-triboelectrically charged by contact with the carrier particles 20. As a result, the toner particles 10 with a charge amount less than the desired value and the reversely charged toner particles 10 can be reduced, and an image with less fogging can be formed.

[0021] Here, the non-coated region A2 is dispersed on the surface of the carrier particles 20. When the coating region A1 and the toner particles 10 existing around the non-coated region A2 come into contact, the toner particles 10 can be triboelectrically charged to a desired charge amount. However, when the coating rate of the carrier core 21 is less than 80.0%, the coating region A1 becomes too narrow. For this reason, even when contacting the carrier particles 20, it is difficult for the toner particles 10 to be triboelectrically charged to a desired charge amount. When the coating rate of the carrier core 21 is 80.0% or more, the carrier particles 20 can triboelectrically charge the toner particles 10 to a desired charge amount by contact with the toner particles 10. As a result, the toner particles 10 with a charge amount less than the desired value and the reversely charged toner particles 10 can be reduced, and an image with less fogging can be formed. Further, when the coating rate of the carrier core 21 is 80.0% or more, the occurrence of carrier development is suppressed.

[0022] In the developer 1 according to the present embodiment, the external additive particles 12 of the toner particles 10 include large-diameter silica particles 13. Since the coating layer 22 contains hard barium titanate particles 23, the carrier particles 20 are relatively hard. The large-diameter silica particles 13 having a number-average primary particle diameter of 30 nm or more function as spacers when the toner particles 10 and the carrier particles 20 come into contact. For this reason, even when the carrier particles 20 are relatively hard, the external additive particles 12 (for example, the large-diameter silica particles 13 and other external additive particles 14 described later) are difficult to be buried in the surface of the toner mother particles 11 by contact with the carrier particles 20, and it is possible to suppress the charge amount of the toner particles 10 from becoming lower than the desired value. For this reason, an image with less fogging can be formed. On the other hand, when the number-average primary particle diameter of the large-diameter silica particles 13 is 120 nm or less, the large-diameter silica particles 13 are difficult to detach from the toner mother particles 11, the variation in the charge amount of the toner can be reduced, and an image with a desired image density can be stably formed. Further, the toner particles 10 with a charge amount less than the desired value and the reversely charged toner particles 10 can be reduced, and an image with less fogging can be formed.

[0023] As described above, the reasons why the developer 1 according to the present embodiment is excellent in anti-fogging property, can stably form an image with a desired image density, can suppress the occurrence of carrier development, and is less likely to cause image defects due to poor cleaning have been explained.

[0024] Furthermore, in addition to the above effects, according to the developer 1 according to the present embodiment, since the coating layer 22 contains hard barium titanate particles 23, the abrasion of the coating layer 22 is reduced, and the long life of the carrier particles 20 can be achieved. Next, the toner and the carrier contained in the developer 1 will be described in more detail.

[0025] [Toner] The toner contains toner particles 10. The toner particles 10 have a toner mother particle 11 and external additive particles 12. The external additive particles 12 are provided on the surface of the toner mother particle 11. Hereinafter, the external additive particles 12 and the toner mother particle 11 will be described.

[0026] [External additive particles] The external additive particles 12 include large-diameter silica particles 13. The external additive particles 12 may further include external additive particles other than the large-diameter silica particles 13 (hereinafter sometimes referred to as other external additive particles) 14 as necessary. Hereinafter, the large-diameter silica particles 13 and the other external additive particles 14 will be described.

[0027] (Large-diameter silica particles) As already described, the number-average primary particle diameter of the large-diameter silica particles 13 is 30 nm or more and 120 nm or less. In order to form an image with less fogging and having a desired image density stably, the number-average primary particle diameter of the large-diameter silica particles 13 is preferably 40 nm or more, more preferably 60 nm or more, still more preferably 80 nm or more, and particularly preferably 100 nm or more. The number-average primary particle diameter of the large-diameter silica particles 13 can be measured, for example, using a scanning electron microscope.

[0028] Examples of the large-diameter silica particles 13 include sol-gel silica particles and fumed silica particles.

[0029] Zirconia silica particles, also called wet silica and particles, are synthesized, for example, in a liquid. Since the zirconia silica particles are grown in a liquid during synthesis, the number average primary particle diameter of the zirconia silica particles is relatively large. When using zirconia silica particles as the large-diameter silica particles 13, the longer the reaction time during synthesis, the larger the number average primary particle diameter of the zirconia silica particles tends to be.

[0030] Fumed silica particles, also called dry silica particles, are produced, for example, by the combustion of silicon tetrachloride. In an example of a method for producing fumed silica particles, a mixed raw material of silicon tetrachloride, a reducing agent, and water is heated to generate silicon dioxide gas, and the silicon dioxide gas is cooled by blowing in cooling air to deposit fumed silica particles. The heating temperature of the mixed raw material is preferably 1000 °C or higher and 2000 °C or lower. The smaller the flow rate of the blown cooling air, the larger the number average primary particle diameter of the fumed silica particles tends to be. The flow rate of the cooling air is 3 / hour or more and 150 m 3 / hour or less, preferably 80 m 3 / hour or more and 110 m 3 / hour or less is more preferable. Table 1 shows reaction examples (1-A) to (1-C). Reaction examples (1-A) to (1-C) show the relationship between the flow rate of the cooling air and the number average primary particle diameter of the obtained large-diameter silica particles 13 when the heating temperature of the mixed raw material is 1800 °C. In Table 1, "diameter" indicates the number average primary particle diameter of the large-diameter silica particles 13.

[0031]

Table 1

[0032] The large-diameter silica particles 13 may be produced, for example, by binding silica particles to each other using at least one selected from the group consisting of silicone and silane coupling agents to obtain a bound product, and then crushing the bound product. The large-diameter silica particles 13 produced in this way are, for example, composite particles (bound product particles) of a plurality of silica particles and a binder. In this composite particle, the binder is located between a plurality of silica particles, and the binder is at least one selected from the group consisting of silicone and silane coupling agents. Examples of silicone include dimethylpolysiloxane. Examples of silane coupling agents include silane coupling agents having an amino group, and more specifically, 3-aminopropyltrimethoxysilane and aminopropylethoxysilane. The temperature at which the silica particles are bound to each other is preferably 50°C or higher and 200°C or lower. For crushing the bound product, for example, a jet mill is used. The larger the air volume of the jet mill when crushing the bound product, the larger the number-average primary particle diameter of the large-diameter silica particles 13. The air volume of the jet mill when crushing the bound product is preferably 1.2 m 3 / min or more and 2.0 m 3 / min or less, and more preferably 1.2 m 3 / min or more and 1.5 m 3 / min or less. Table 2 shows reaction examples (2-A) to (2-D). Reaction examples (2-A) to (2-D) show the relationship between the air volume of the jet mill when crushing the bound product and the number-average primary particle diameter of the obtained large-diameter silica particles 13. In Table 2, "diameter" indicates the number-average primary particle diameter of the large-diameter silica particles 13.

[0033]

Table 2

[0034] The large-diameter silica particles 13 may be surface-treated. For example, hydrophobicity and / or positive charge may be imparted to the surface of the large-diameter silica particles 13 by a surface treatment agent. Examples of the surface treatment agent that can be used for surface treatment include silicone oil and silane coupling agents (e.g., 3-aminopropyltrimethoxysilane, aminopropylethoxysilane).

[0035] The bulk density of the large-diameter silica particles 13 is preferably 0.1 g / cm 3 or more and 1.0 g / cm 3 or less. The true specific gravity of the large-diameter silica particles 13 is preferably 1.0 or more and 2.0 or less. The BET specific surface area of the large-diameter silica particles 13 is preferably 20 m 2 / g or more and 60 m 2 / g or less. The degree of hydrophobization of the large-diameter silica particles 13 is preferably 50% or more and 80% or less.

[0036] The amount of the large-diameter silica particles 13 is preferably 0.1 part by mass or more and 10.0 parts by mass or less, more preferably 0.4 part by mass or more and 1.0 part by mass or less, based on 100.0 parts by mass of the toner mother particles 11.

[0037] (Other externally added agent particles) Examples of the other externally added agent particles 14 include alumina particles, magnesium oxide particles, zinc oxide particles, and silica particles having a number-average primary particle diameter of less than 30 nm. Hereinafter, the "silica particles having a number-average primary particle diameter of less than 30 nm" may be referred to as "small-diameter silica particles".

[0038] The number average primary particle diameter of the small-diameter silica particles is preferably 5 nm or more and 25 nm or less. The surface of the small-diameter silica particles may be imparted with hydrophobicity and / or positive chargeability by a surface treatment agent. Examples of the small-diameter silica particles include fumed silica particles. Since it is not necessary to increase the number average primary particle diameter of the small-diameter silica particles, they do not have to be composite particles (agglomerated particles) of a plurality of silica particles and a binder. For example, the small-diameter silica particles may be silica particles composed only of silica (e.g., fumed silica), or silica particles having a silica core composed only of silica (e.g., fumed silica) and a surface treatment layer by a surface treatment agent.

[0039] When small-diameter silica particles are used as the other externally added agent particles 14, the amount of the large-diameter silica particles 13 is preferably 0.4 part by mass or more and 1.0 part by mass or less with respect to 1.5 parts by mass of the small-diameter silica particles.

[0040] The number average primary particle diameter of the other externally added agent particles 14 other than the small-diameter silica particles is preferably 1 nm or more and 60 nm or less, and more preferably 5 nm or more and 25 nm or less.

[0041] The amount of the other externally added agent particles 14 is preferably 0.1 part by mass or more and 10.0 parts by mass or less, and more preferably 1.0 part by mass or more and 2.0 parts by mass or less with respect to 100.0 parts by mass of the toner base particles 11. The amount of the large-diameter silica particles 13 is preferably 0.4 part by mass or more and 1.0 part by mass or less with respect to 1.5 parts by mass of the other externally added agent particles 14.

[0042] <Toner base particles> The toner base particles 11 contain, for example, at least one selected from the group consisting of a binder resin, a colorant, a charge control agent, and a release agent. Hereinafter, the binder resin, the colorant, the charge control agent, and the release agent will be described.

[0043] (Binder resin) In order to obtain a toner with excellent low-temperature fixability, it is preferable that the toner mother particles 11 contain a thermoplastic resin as the binder resin, and it is more preferable to contain the thermoplastic resin at a ratio of 85% by mass or more of the total binder resin. Examples of the thermoplastic resin include polyester resins, styrene resins, acrylic ester resins (more specifically, acrylic ester polymers, methacrylic ester polymers, etc.), olefin resins (more specifically, polyethylene resins, polypropylene resins, etc.), vinyl resins (more specifically, vinyl chloride resins, polyvinyl alcohol, vinyl ether resins, N-vinyl resins, etc.), polyamide resins, and urethane resins. Further, copolymers of these resins, that is, copolymers in which arbitrary repeating units are introduced into the above resins (more specifically, styrene-acrylic resins, styrene-butadiene resins, etc.) can also be used as the binder resin.

[0044] As the binder resin, a polyester resin is preferable. The polyester resin is a polymer of one or more polyhydric alcohol monomers and one or more polyvalent carboxylic acid monomers. Note that instead of the polyvalent carboxylic acid monomer, a polyvalent carboxylic acid derivative (more specifically, an anhydride of a polyvalent carboxylic acid, a polyvalent carboxylic acid halide, etc.) may be used.

[0045] Examples of the polyhydric alcohol monomer include diol monomers, bisphenol monomers, and polyhydric alcohol monomers having three or more valences.

[0046] Examples of the diol monomer include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-butene-1,4-diol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,4-benzenediol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0047] Examples of bisphenol monomers include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct, and bisphenol A propylene oxide adduct.

[0048] Examples of trihydric or higher alcohols monomers include sorbitol, 1,2,3,6 - hexanetetrol, 1,4 - sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4 - butanetriol, 1,2,5 - pentanetriol, glycerol, diglycerol, 2 - methylpropanetriol, 2 - methyl - 1,2,4 - butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5 - trihydroxymethylbenzene.

[0049] Examples of polyvalent carboxylic acid monomers include divalent carboxylic acid monomers and trivalent or higher carboxylic acid monomers.

[0050] Examples of divalent carboxylic acid monomers include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, 5 - sulfoisophthalic acid, sodium 5 - sulfoisophthalate, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, succinic acid, alkyl succinic acid, and alkenyl succinic acid. Examples of alkyl succinic acid include n - butyl succinic acid, isobutyl succinic acid, n - octyl succinic acid, n - dodecyl succinic acid, and isododecyl succinic acid. Examples of alkenyl succinic acid include n - butenyl succinic acid, isobutenyl succinic acid, n - octenyl succinic acid, n - dodecenyl succinic acid, and isododecenyl succinic acid.

[0051] Examples of carboxylic acid monomers having a valency of 3 or more include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and Empol trimer acid.

[0052] The polyester resin is preferably a polymer of a bisphenol monomer, a divalent carboxylic acid monomer, and a trivalent carboxylic acid monomer. The polyester resin is more preferably a polymer of a bisphenol A alkylene oxide adduct, a dicarboxylic acid having 3 to 6 carbon atoms, and an aryltricarboxylic acid. The polyester resin is even more preferably a polymer of a bisphenol A ethylene oxide adduct, a bisphenol A propylene oxide adduct, fumaric acid, and trimellitic acid.

[0053] The polyester resin is preferably an amorphous polyester resin. For amorphous polyester resins, it is often not possible to measure a distinct melting point. Therefore, a polyester resin that cannot be judged to have a distinct endothermic peak in the endothermic curve measured using a differential scanning calorimeter can be judged as an amorphous polyester resin without problem.

[0054] The softening point of the polyester resin is preferably 50°C or higher and 200°C or lower, and more preferably 80°C or higher and 120°C or lower. The glass transition point of the polyester resin is preferably 40°C or higher and 100°C or lower, and more preferably 40°C or higher and 60°C or lower.

[0055] The mass average molecular weight of the polyester resin is preferably 10,000 or more and 50,000 or less, and more preferably 20,000 or more and 40,000 or less.

[0056] The acid value of the polyester resin is preferably 1 mgKOH / g or more and 30 mgKOH / g or less, more preferably 10 mgKOH / g or more and 20 mgKOH / g or less. The hydroxyl value of the polyester resin is preferably 1 mgKOH / g or more and 50 mgKOH / g or less, more preferably 20 mgKOH / g or more and 40 mgKOH / g or less.

[0057] The amount of the binder resin is preferably 85 parts by mass or more and 95 parts by mass or less with respect to 100 parts by mass of the toner mother particles 11.

[0058] (Colorant) As the colorant, known pigments or dyes can be used according to the color of the toner. Examples of the colorant include, for example, black colorants, yellow colorants, magenta colorants, and cyan colorants.

[0059] Examples of the black colorant include carbon black. The black colorant may also be a colorant toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

[0060] As the yellow colorant, for example, one or more compounds selected from the group consisting of condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds can be used. Examples of the yellow colorant include, for example, C.I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155, 168, 174, 175, 176, 180, 181, 191, and 194), naphthol yellow S, Hansa yellow G, and C.I. Vat Yellow.

[0061] As the magenta colorant, for example, one or more compounds selected from the group consisting of condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds can be used. Examples of the magenta colorant include C.I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48:2, 48:3, 48:4, 57:1, 81:1, 122, 144, 146, 150, 166, 169, 177, 184, 185, 202, 206, 220, 221, and 254).

[0062] As the cyan colorant, for example, one or more compounds selected from the group consisting of copper phthalocyanine compounds, anthraquinone compounds, and basic dye lake compounds can be used. Examples of the cyan colorant include C.I. Pigment Blue (1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, and 66), phthalocyanine blue, C.I. Vat Blue, and C.I. Acid Blue.

[0063] The amount of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

[0064] (Charge control agent) The charge control agent is used, for example, for the purpose of obtaining a toner having excellent charging stability and charging rise characteristics. The charging rise characteristics of the toner serve as an index of whether the toner can be charged to a predetermined charge level in a short time. Examples of the charge control agent include a positive charge control agent and a negative charge control agent. By incorporating a positive charge control agent into the toner mother particles 11, the cationicity (positive chargeability) of the toner can be enhanced, and by incorporating a negative charge control agent into the toner mother particles 11, the anionicity (negative chargeability) of the toner can be enhanced. Examples of the positive charge control agent include pyridine, nigrosine, and quaternary ammonium salts. Examples of the negative charge control agent include metal-containing azo dyes, sulfonic group-containing resins, oil-soluble dyes, naphthenic acid metal salts, acetylacetone metal complexes, salicylic acid-based metal complexes, boron compounds, fatty acid soaps, and long-chain alkyl carboxylates. However, when sufficient chargeability is ensured in the toner, it is not necessary to incorporate a charge control agent into the toner mother particles 11. The amount of the charge control agent is preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the binder resin.

[0065] (Release agent) The release agent is used, for example, for the purpose of obtaining a toner with excellent hot offset resistance. Examples of the release agent include aliphatic hydrocarbon waxes, oxides of aliphatic hydrocarbon waxes, plant-derived waxes, animal-derived waxes, mineral-derived waxes, ester waxes mainly composed of fatty acid esters, and waxes in which part or all of the fatty acid esters have been deoxidized. Examples of the aliphatic hydrocarbon waxes include polyethylene wax (e.g., low molecular weight polyethylene), polypropylene wax (e.g., low molecular weight polypropylene), polyolefin copolymers, polyolefin waxes, microcrystalline waxes, paraffin waxes, and Fischer-Tropsch waxes. Examples of the oxides of aliphatic hydrocarbon waxes include polyethylene oxide wax and block copolymers of polyethylene oxide wax. Examples of the plant-derived waxes include candelilla wax, carnauba wax, wood wax, jojoba wax, and rice wax. Examples of the animal-derived waxes include beeswax, lanolin, and spermaceti wax. Examples of the mineral-derived waxes include ozokerite, ceresin, and petrolatum. Examples of the ester waxes mainly composed of fatty acid esters include montanic acid ester wax and castor wax. Examples of the waxes in which part or all of the fatty acid esters have been deoxidized include deacidified carnauba wax. The amount of the release agent is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

[0066] Note that the toner particles 10 may contain known additives as necessary. The volume median diameter of the toner particles 10 is preferably 4 μm or more and 12 μm or less. The volume median diameter of the toner mother particles 11 is preferably 4 μm or more and 12 μm or less, and more preferably 5 μm or more and 9 μm or less. The toner particles 10 may be magnetic toner or non-magnetic toner. When the toner particles 10 are magnetic toner, magnetic powder is further contained in the toner mother particles 11. In the developer 1, the amount of toner is preferably 1 part by mass or more and 15 parts by mass or less, and more preferably 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the carrier. For ease of explanation, non-capsule toner mother particles 11 are shown in FIG. 1. However, it may be capsule toner mother particles having the toner mother particles 11 shown in FIG. 1 as a toner core and a shell layer covering the toner core. The above is the description of the toner.

[0067] [Carrier] The carrier includes carrier particles 20. The carrier particles 20 have a carrier core 21 and a coat layer 22. The coat layer 22 covers the surface of the carrier core 21. The coat layer 22 is provided on the surface of the carrier core 21.

[0068] As already described, the coat layer / core ratio is 0.09% by mass or more and 4.90% by mass or less. The coat layer / core ratio is preferably 0.11% by mass or more. The coat layer / core ratio is preferably 4.40% by mass or less, more preferably 4.00% by mass or less, still more preferably 3.00% by mass or less, even more preferably 2.00% by mass or less, still even more preferably 1.40% by mass or less, yet even more preferably 1.00% by mass or less, particularly preferably 0.90% by mass or less, particularly even more preferably 0.50% by mass or less, more particularly preferably 0.25% by mass or less, especially preferably 0.24% by mass or less, and particularly even more preferably 0.20% by mass or less.

[0069] The ratio of the mass of the coating resin to the mass of the carrier core 21 is preferably 0.05% by mass or more and 4.00% by mass or less. Hereinafter, the "ratio of the mass of the coating resin to the mass of the carrier core 21" may be referred to as the "resin / core ratio". The resin / core ratio is preferably 0.07% by mass or more. The resin / core ratio is preferably 3.00% by mass or less, more preferably 2.50% by mass or less, still more preferably 2.00% by mass or less, even still more preferably 1.40% by mass or less, yet even still more preferably 1.00% by mass or less, particularly preferably 0.90% by mass or less, particularly even still more preferably 0.50% by mass or less, even more preferably 0.25% by mass or less, particularly preferably 0.24% by mass or less, and particularly even still more preferably 0.20% by mass or less.

[0070] The coverage rate of the carrier core 21 is the ratio of the area of the coated region A1 covered by the coating layer 22 to the area of the surface of the carrier core 21. The coverage rate of the carrier core 21 is obtained from the surface image of the carrier core 21 taken using a scanning electron microscope by determining the area of the coated region A1 appearing in the surface image and the area of the non-coated region A2 appearing in the surface image, and is calculated according to the formula "coverage rate = 100 × area of coated region A1 / area of surface of carrier core 21 = 100 × area of coated region A1 / total area of coated region A1 and non-coated region A2". The method for adjusting the coverage rate of the carrier core 21 will be described in the <carrier formation step> described later.

[0071] The coverage rate of the carrier core 21 is the average value calculated from the formula "coverage rate = total coverage rate of the measured carrier cores 21 / number of the measured carrier cores 21" by measuring the coverage rates of a substantial number (for example, 100) of carrier cores 21 included in the carrier. As already described, the coverage rate of the carrier core 21 is 80.0% or more and less than 100.0%. In order to form an image with less fogging, the coverage rate of the carrier core 21 is preferably 85.0% or more, more preferably 90.0% or more, even more preferably exceeding 90.0%, still more preferably 92.0% or more, even more preferably 95.0% or more, and particularly preferably 96.0% or more. In order to form an image with less fogging, the coverage rate of the carrier core 21 is preferably 99.0% or less.

[0072] To charge the toner to a desired charge amount and form an image with less fogging, the BET specific surface area of the carrier particles 20 is preferably 0.3 m 2 / g or more and 3.5 m 2 / g or less, and more preferably 0.3 m 2 / g or more and 3.0 m 2 / g or less. The BET specific surface area of the carrier particles 20 is determined from the adsorption amount of liquid nitrogen adsorbed on the surface of the carrier particles 20 using an automatic specific surface area measuring device based on the BET method (nitrogen adsorption specific surface area method).

[0073] The shape factor of the carrier particles 20 is calculated from the formula "shape factor of the carrier particles 20 = measured carrier particle diameter / calculated carrier particle diameter". The calculated carrier particle diameter in the above formula is calculated from the formula "calculated carrier particle diameter = 6 / (true specific gravity of the carrier particles 20 × BET specific surface area of the carrier particles 20)". The shape factor of the carrier particles 20 is measured, for example, by the method described in the examples.

[0074] The shape factor of the carrier particles 20 is preferably 7.0 or more and 55.0 or less. The closer the shape factor of the carrier particles 20 is to 1.0, the closer the shape of the carrier particles 20 is to a perfect sphere, and the unevenness on the surface of the carrier particles 20 becomes smaller. When the shape factor of the carrier particles 20 is 7.0 or more, the unevenness on the surface of the carrier particles 20 becomes moderately large, and the concave portions on the surface of the carrier particles 20 capture the externally added agent particles 12 detached from the toner particles 10. Therefore, the influence of the detached externally added agent particles 12 is reduced, and the carrier particles 20 can charge the toner particles 10 to a desired charge amount. On the other hand, when the shape factor of the carrier particles 20 is 55.0 or less, the coating layer 22 tends to be formed in a dispersed state rather than an aggregated state on the surface of the carrier particles 20. Therefore, the fluidity of the carrier particles 20 is improved, and the toner particles 10 tend to be charged to a desired charge amount in a short time by contact with the carrier particles 20. The method for adjusting the shape factor of the carrier particles 20 will be described in the <Carrier Formation Step> described later.

[0075] The ratio of the coverage rate of the carrier core 21 to the shape factor of the carrier particles 20 is preferably 1.9 or more and 11.5 or less. Hereinafter, the "ratio of the coverage rate of the carrier core 21 to the shape factor of the carrier particles 20" may be described as "ratio (coverage rate / shape factor)". The ratio (coverage rate / shape factor) is calculated from the formula "ratio (coverage rate / shape factor) = coverage rate of the carrier core 21 / shape factor of the carrier particles 20". The coverage rate of the carrier core 21 and the shape factor of the carrier particles 20 are measured, for example, by the method described in the examples.

[0076] The higher the ratio (coating rate / shape factor), the higher the coating rate of the carrier core 21 and the smaller the shape factor of the carrier particles 20 (the unevenness on the surface of the carrier particles 20 tends to be smaller). When the ratio (coating rate / shape factor) is 1.9 or more and 11.5 or less, the balance between the coating rate of the carrier core 21 and the shape factor of the carrier particles 20 is good, and the carrier particles 20 can impart a sufficient amount of charge to the toner particles 10. For this reason, the toner particles 10 with a charge amount less than the desired value and the reversely charged toner particles 10 are reduced, and an image with less fogging can be formed. When the ratio (coating rate / shape factor) is 11.5 or less, when forming an image with a low printing rate (for example, a printing rate of about 5%), there is a tendency to form an image with particularly less fogging. Further, when the ratio (coating rate / shape factor) is 1.9 or more, in addition to the case of a low printing rate, when forming an image with a high printing rate (for example, a printing rate of 30% or more), there is a tendency to form an image with particularly less fogging.

[0077] Next, the carrier core 21 and the coating layer 22 of the carrier particles 20 will be described.

[0078] <Carrier Core> The carrier core 21 contains, for example, a magnetic material. Examples of the magnetic material contained in the carrier core 21 include metal oxides, and more specifically, magnetite, maghemite, and ferrite. Ferrite tends to have high fluidity and chemical stability. For this reason, from the viewpoint of forming a high-quality image over a long period, it is preferable that the carrier core 21 contains ferrite. Examples of ferrite include barium ferrite, manganese ferrite (Mn-ferrite), Mn-Zn ferrite, Ni-Zn ferrite, Mn-Mg ferrite, Ca-Mg ferrite, Li ferrite, and Cu-Zn ferrite. The shape of the carrier core 21 is not particularly limited, and it may be an irregular shape or a spherical shape. As the carrier core 21, a commercially available product may be used. Alternatively, the carrier core 21 may be made by pulverizing and firing a magnetic material.

[0079] The volume median diameter of the carrier core 21 is preferably 20.0 μm or more, more preferably 25.0 μm or more. When the volume median diameter of the carrier core 21 is 20.0 μm or more, carrier development is less likely to occur. As a result, it is possible to suppress the transfer of the carrier particles 20 attached to the photoreceptor drum to the transfer section, and it is possible to suppress the occurrence of image defects such as transfer omission. On the other hand, the volume median diameter of the carrier core 21 is preferably 80.0 μm or less, more preferably 65.0 μm or less, still more preferably 60.0 μm or less, even more preferably 50.0 μm or less, still more preferably less than 40.0 μm, and particularly preferably 35.0 μm or less. When the volume median diameter of the carrier core 21 is 80.0 μm or less, the magnetic brush of the developer 1 formed on the peripheral surface of the developing roller during image formation becomes finer, and a finely grained image can be formed. The volume median diameter of the carrier core 21 is measured, for example, by the method described in the examples.

[0080] The saturation magnetization of the carrier core 21 is preferably 65 emu / g or more and 90 emu / g or less, more preferably 70 emu / g or more and 85 emu / g or less. When the saturation magnetization of the carrier core 21 is 65 emu / g or more, carrier development is less likely to occur. When the saturation magnetization of the carrier core 21 is 90 emu / g or less, the magnetic brush of the developer 1 formed on the peripheral surface of the developing roller during image formation becomes finer, and a finely grained image can be formed. When the carrier core 21 contains Mn-ferrite, the saturation magnetization of the carrier core 21 tends to decrease as the Mn content increases. Further, when the carrier core 21 contains Mn-Mg ferrite, the saturation magnetization of the carrier core 21 tends to decrease as the Mg content increases. The saturation magnetization of the carrier core 21 is measured, for example, by the method described in the examples.

[0081] The apparent density of the carrier core 21 is 1.20×10 3 kg / m 3 or more and 2.80×10 3 kg / m 3The following are preferred. The fluidity of the carrier core 21 is preferably 21 seconds / 50 g or more and 50 seconds / 50 g or less. The electrical resistivity of the carrier core 21 is preferably 1×10 2 Ω·m or more and 1×10 7 Ω·m or less. The residual magnetization of the carrier core 21 is preferably 0.4 Am 2 / kg or more and 10.0 Am 2 / kg or less. The coercive force of the carrier core 21 is preferably 5 A / m·10 3 / 4π or more and 10 A / m·10 3 / 4π or less.

[0082] <Coating layer> The coating layer 22 includes a coating resin and barium titanate particles 23. The coating layer 22 preferably further includes carbon black particles 24. However, the carbon black particles 24 may not be contained. The coating layer 22 has a coating resin region 25. The coating resin region 25 is composed of the coating resin. The coating resin region 25 is a region containing only the coating resin. The coating layer 22 has, for example, barium titanate particles 23, carbon black particles 24, and a coating resin region 25 existing around these. Hereinafter, the coating resin, barium titanate particles 23, and carbon black particles 24 will be described.

[0083] (Coating resin) The coating resin includes a silicone resin. By including a silicone resin in the coating resin, the toner can be favorably triboelectrically charged to a desired charge amount. Also, by using a silicone resin as the coating resin, a thinner coating layer 22 can be formed as compared with resins other than the silicone resin (for example, fluororesin). Thereby, the amount of the coating resin contained in the coating layer 22 can be reduced, and the influence on triboelectric charging caused by the moisture-absorbed coating resin (for example, the influence that the triboelectric charge amount of the toner particles 10 decreases) can be reduced.

[0084] Preferable examples of the silicone resin include a silicone resin having a methyl group and an epoxy resin-modified silicone resin. An example of the silicone resin having a methyl group is a silicone resin having a methyl group and no phenyl group. Another example of the silicone resin having a methyl group is a silicone resin having a methyl group and a phenyl group (hereinafter sometimes referred to as "methylphenyl silicone resin"). The coating layer 22 may contain only a silicone resin as the coating resin, or may further contain a resin other than the silicone resin.

[0085] (Barium titanate particles) As already described, the number average primary particle diameter of the barium titanate particles 23 is 100 nm or more and 500 nm or less. In order to form an image with less blooming, the number average primary particle diameter of the barium titanate particles 23 is preferably 200 nm or more. In order to suppress the occurrence of image defects due to poor cleaning, the number average primary particle diameter of the barium titanate particles 23 is preferably 400 nm or less. The number average primary particle diameter of the barium titanate particles 23 is measured, for example, by the method described in the examples.

[0086] As already described, the content of the barium titanate particles 23 is 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coating resin. The content of the barium titanate particles 23 is preferably 25 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coating resin. When the coating resin contains two or more resins, 100 parts by mass of the coating resin means that the total mass of the two or more resins is 100 parts by mass.

[0087] The method for manufacturing the barium titanate particles 23 is not particularly limited, and examples thereof include the hydrothermal synthesis method and the oxalate method. The method for manufacturing the barium titanate particles 23 is preferably the hydrothermal synthesis method. That is, it is preferable that the barium titanate particles 23 are hydrothermal synthesis products. The true specific gravity of the barium titanate particles 23 produced by the hydrothermal synthesis method is smaller than that of the barium titanate particles 23 produced by the oxalate method because they have voids inside. In addition, the particle size distribution of the barium titanate particles 23 produced by the hydrothermal synthesis method is sharp. For these reasons, the barium titanate particles 23 produced by the hydrothermal synthesis method are easily and uniformly dispersed in the coating resin, and a carrier having a high charge imparting ability is easily obtained. As a result, due to the friction with the carrier, the toner is quickly charged, and an image with less fogging can be obtained.

[0088] The hydrothermal synthesis method has, for example, a hydrothermal reaction step and a heat treatment step. In the hydrothermal reaction step, a water-soluble barium salt is added to a titanium oxide dispersion liquid in which titanium oxide particles are dispersed, and hydrothermal reaction is carried out by heating. In this way, barium titanate hydrothermal synthesis particles are obtained. In the heat treatment step, the barium titanate hydrothermal synthesis particles are heat-treated to obtain the barium titanate particles 23. The heating temperature in the hydrothermal reaction step is preferably 80°C or higher. The heat treatment temperature in the heat treatment step is preferably 650°C or higher and 850°C or lower. The number average primary particle diameter of the barium titanate particles 23 can be adjusted, for example, by changing the heating temperature and the time for carrying out the hydrothermal reaction in the hydrothermal reaction step. For example, the higher the heating temperature in the hydrothermal reaction step, the larger the number average primary particle diameter of the barium titanate particles 23. Also, the longer the time for carrying out the hydrothermal reaction, the larger the number average primary particle diameter of the barium titanate particles 23.

[0089] (Carbon black particles) The carbon black particles 24 are conductors. Therefore, since the coating layer 22 contains the carbon black particles 24, charges can smoothly move from the carrier particles 20 to the toner particles 10. As a result, the toner particles 10 can be charged to a desired charge amount, and an image with less fogging can be formed. Further, even when the toner concentration in the developer 1 changes, fluctuations in the charge amount of the toner can be reduced, and an image with a desired image density can be stably formed.

[0090] The number average primary particle diameter of the carbon black particles 24 is preferably 10 nm or more and 50 nm or less, more preferably 20 nm or more and 40 nm or less. The DBP oil absorption amount of the carbon black particles 24 is 3 preferably 50 cm 3 / 100 g or more and 700 cm 3 / 100 g or less, more preferably 100 cm 3 / 100 g or more and 600 cm 2 / 100 g or less. The BET specific surface area of the carbon black particles 24 is 2 preferably 100 m 2 / g or more and 2000 m 2 / g or less, more preferably 100 m 2 / g or more and 200 m 2 / g or less, or 1200 m

[0091] Since the coating layer 22 contains the barium titanate particles 23, the electrical resistance of the carrier particles 20 is appropriately reduced. Therefore, even if the amount of the carbon black particles 24 which are conductors is small, the electrical resistance of the carrier particles 20 is appropriately reduced. Since the amount of the carbon black particles 24 can be reduced, it is possible to suppress the occurrence of color turbidity in an image formed using the developer 1 containing the carrier particles 20. The amount of the carbon black particles 24 is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 3 parts by mass or more and 9 parts by mass or less, still more preferably 3 parts by mass or more and 6 parts by mass or less or 6 parts by mass or more and 9 parts by mass or less with respect to 100 parts by mass of the coating resin.

[0092] Note that the carrier particles 20 may contain known additives as required. The volume median diameter of the carrier particles 20 is preferably 25 μm or more and 100 μm or less. The above is the description of the carrier.

[0093] [Method for manufacturing developer] Hereinafter, an example of the method for manufacturing the developer 1 according to the present embodiment will be described. The method for manufacturing the developer 1 according to the present embodiment includes, for example, a toner forming step, a carrier forming step, and a step of mixing the toner and the carrier.

[0094] <Toner forming step> In the toner forming step, for example, a binder resin, a colorant, a charge control agent, and a release agent are mixed to obtain a mixture. The mixture is melt-kneaded to obtain a melt-kneaded product. The melt-kneaded product is pulverized to obtain a pulverized product. The pulverized product is classified to obtain toner mother particles 11. Using a mixer, the toner mother particles 11 and the external additive particles 12 (large-diameter silica particles 13 and other external additive particles 14) are mixed. By mixing, the external additive particles 12 adhere to the surface of the toner mother particles 11 to obtain a toner containing toner particles 10. The mixing with the external additive particles 12 is preferably carried out under the condition that the external additive particles 12 are not completely buried in the toner mother particles 11. The external additive particles 12 are attached to the surface of the toner mother particles 11 by physical bonding (physical force) rather than chemical bonding.

[0095] <Carrier forming step> In the carrier formation step, a coating layer 22 is formed on the surface of the carrier core 21 to obtain a carrier containing carrier particles 20. For example, a coating liquid containing a coating resin, barium titanate particles 23, and optional carbon black particles 24 is sprayed onto the carrier core 21 in a fluidized bed. Next, the carrier core 21 sprayed with the coating liquid is heated at a first predetermined temperature (hereinafter sometimes referred to as the predetermined drying temperature) to dry the coating liquid adhering to the surface of the carrier core 21 and obtain a dried product. Then, using an electric furnace, the dried product is heated at a second predetermined temperature (hereinafter sometimes referred to as the predetermined firing temperature) to cure the coating resin contained in the coating liquid on the surface of the carrier core 21. In this way, the coating layer 22 is formed on the surface of the carrier core 21. The predetermined drying temperature is preferably 70°C or higher and 80°C or lower. The predetermined firing temperature is preferably 200°C or higher and 300°C or lower.

[0096] The coverage rate of the carrier core 21 and the shape factor of the carrier particles 20 can be adjusted, for example, by changing the predetermined drying temperature and the amount of the coating liquid sprayed onto the carrier core 21. The higher the predetermined drying temperature, the more the coating liquid dries before spreading over the entire surface of the carrier core 21. For this reason, the higher the predetermined drying temperature, the coating layer 22 is formed on a part of the surface rather than the entire surface of the carrier core 21, the coverage rate of the carrier core 21 decreases, and the shape factor of the carrier particles 20 tends to increase. Also, the smaller the amount of the coating liquid sprayed onto the carrier core 21, the more likely the coverage rate of the carrier core 21 is to decrease.

[0097] <Mixing step of toner and carrier> In the mixing step of toner and carrier, the developer 1 is obtained by mixing toner and carrier using a mixer.

Example

[0098] Hereinafter, the present invention will be described more specifically using examples. However, the present invention is not limited to the scope of the examples at all.

[0099] <Preparation of carrier> Carriers (CA-1) to (CA-23) and (CB-1) to (CB-8) were prepared. The compositions of these carriers are shown in Tables 3 to 6 described below. Carriers (CA-1) to (CA-23) and (CB-1) to (CB-8) were used for the preparation of developers (A-1) to (A-23) and (B-1) to (B-8), respectively. For the sake of understanding, in Tables 3 to 6, carriers having the same composition are also indicated by different carrier numbers corresponding to the developer numbers.

[0100] (Preparation of Carrier (CA-1)) 60.00 g of a silicone resin solution (“KR-255” manufactured by Shin-Etsu Chemical Co., Ltd., solid content concentration: 50% by mass, solid content: 30.00 g), 1.50 g of barium titanate (“BT-01” manufactured by Sakai Chemical Industry Co., Ltd., barium titanate produced by the hydrothermal synthesis method, number average primary particle diameter: 102 nm), 0.90 g of carbon black (“Ketjenblack EC300J” manufactured by Lion Specialty Chemicals Co., Ltd.), and 240.00 g of toluene were mixed using a homomixer to obtain a coating solution.

[0101] While flowing 5000 g of carrier cores using a fluidized bed coating apparatus (“FD-MP-01 D type” manufactured by Paurek Co., Ltd.), the coating solution was sprayed onto the carrier cores. In this way, carrier cores coated with the coating solution were obtained. The coating conditions were such that the air supply temperature (corresponding to the predetermined drying temperature described in the embodiment) was 75°C, the air supply volume was 0.3 m 3 / min, and the rotor rotation speed was 400 rpm. As the carrier cores, manganese ferrite cores (manufactured by DOWA IP Creation Co., Ltd., volume median diameter: 20.3 μm, saturation magnetization: 67 emu / g) were used. The carrier cores coated with the coating solution were baked at a temperature of 200°C (corresponding to the predetermined firing temperature described in the embodiment) for 1 hour using an electric furnace. In this way, a coating layer was formed on the surface of the carrier cores to obtain carrier (CA-1).

[0102] (Preparation of Carriers (CA-2) to (CA-23) and (CB-1) to (CB-8)) Carriers (CA-2) to (CA-23) and (CB-1) to (CB-8) were each prepared in the same manner as the preparation of carrier (CA-1), except for the following changes. That is, coating resin solutions of the types shown in Tables 3 to 6 were used in amounts such that the solid content was as shown in Tables 3 to 6. Barium titanate produced by the production methods shown in Tables 3 to 6 and having the number average primary particle diameters shown in Tables 3 to 6 was used in the amounts shown in Tables 3 to 6. Carbon black of the types shown in Tables 3 to 6 was used in the amounts shown in Tables 3 to 6. A carrier core having the volume median diameter shown in Tables 3 to 6 and the saturation magnetization shown in Tables 3 to 6 was used. The supply air temperature of the coating conditions was adjusted so as to achieve the coating rate of the carrier core shown in Tables 3 to 6. Note that the higher the supply air temperature, the lower the coating rate of the carrier core.

[0103] For the coating resins and carbon black shown in Tables 3 to 6, commercially available products were used, and their details will be described later in the explanations of the terms in Tables 3 to 6. For barium titanate produced by the production methods shown in Tables 3 to 6 and having the number average primary particle diameters shown in Tables 3 to 6, the following were used. All carrier cores having the volume median diameter shown in Tables 3 to 6 and the saturation magnetization shown in Tables 3 to 6 were manganese ferrite cores manufactured by DOWA IP Creation Co., Ltd. · Barium titanate (production method: hydrothermal synthesis method, number average primary particle diameter: 102 nm): "BT-01" manufactured by Sakai Chemical Industry Co., Ltd. · Barium titanate (production method: hydrothermal synthesis method, number average primary particle diameter: 304 nm): "BT-03" manufactured by Sakai Chemical Industry Co., Ltd. · Barium titanate (production method: hydrothermal synthesis method, number average primary particle diameter: 495 nm): "BT-05" manufactured by Sakai Chemical Industry Co., Ltd. · Barium titanate (production method: hydrothermal synthesis method, number average primary particle diameter: 76 nm): Particle size adjusted product manufactured by Sakai Chemical Industry Co., Ltd. · Barium titanate (production method: hydrothermal synthesis method, number average primary particle diameter: 687 nm): "BT-07" manufactured by Sakai Chemical Industry Co., Ltd. · Barium titanate (production method: oxalate method, number-average primary particle diameter: 304 nm): 0.3 μm product of "Parceram BT" manufactured by Nippon Chemical Industry Co., Ltd.

[0104] <Silica particles> The following silica particles were prepared for use as an external additive for toner. · Large-diameter silica particles (S1): number-average primary particle diameter 40 nm · Large-diameter silica particles (S2): number-average primary particle diameter 60 nm · Large-diameter silica particles (S4): number-average primary particle diameter 100 nm · Large-diameter silica particles (S5): number-average primary particle diameter 120 nm · Ultra-large-diameter silica particles (S6): number-average primary particle diameter 150 nm · Large-diameter silica particles (S3): "X-24-9600A-80" manufactured by Shin-Etsu Chemical Co., Ltd. (sol-gel silica, number-average primary particle diameter 80 nm, bulk density 0.44 g / cm 3 , true specific gravity 1.8, BET specific surface area 40 m 2 / g, degree of hydrophobicity 67%) · Small-diameter silica particles: "AEROSIL (registered trademark) REA90" manufactured by Nippon Aerosil Co., Ltd. (fumed silica imparted with positive chargeability and hydrophobicity by surface treatment, number-average primary particle diameter 20 nm)

[0105] Note that the above large-diameter silica particles (S1), (S2), (S4), (S5), and (S6) were all particle size-adjusted products of "CAB-O-SIL (registered trademark) TG-5110" manufactured by Cabot Corporation. "CAB-O-SIL (registered trademark) TG-5110" was fumed silica surface-treated with hexamethyldisilazane.

[0106] <Synthesis of amorphous polyester resin (PS1)> An amorphous polyester resin (PS1) for use as a binder resin for toner mother particles of toner was synthesized by the following method. First, a reaction vessel equipped with a thermometer (thermocouple), a dehydrating tube, a nitrogen inlet tube, and a stirring device (stirring blades) was set in an oil bath. Into this reaction vessel, 1575 g of BPA-PO (bisphenol A propylene oxide adduct), 163 g of BPA-EO (bisphenol A ethylene oxide adduct), 377 g of fumaric acid, and 4 g of a catalyst (dibutyltin oxide) were charged. Subsequently, after making the inside of the reaction vessel into a nitrogen atmosphere, while stirring the contents, the temperature inside the reaction vessel was raised to 220 °C using the oil bath. Under the conditions of a nitrogen atmosphere and a temperature of 220 °C, while distilling off the by-produced water, the contents of the reaction vessel were subjected to a polymerization reaction for 8 hours. Subsequently, after reducing the pressure inside the reaction vessel, under the conditions of a reduced pressure atmosphere (pressure: 60 mmHg) and a temperature of 220 °C, the contents of the reaction solution were further subjected to a polymerization reaction for 1 hour. Subsequently, after lowering the temperature inside the reaction vessel to 210 °C, 336 g of trimellitic anhydride was added to the reaction vessel. Then, under the conditions of a reduced pressure atmosphere (pressure: 60 mmHg) and a temperature of 210 °C, the contents of the reaction vessel were reacted. The reaction time in the reaction was adjusted so that the physical property values of the amorphous polyester resin (PS1) as the reaction product would be the following physical properties. Thereafter, by taking out the reaction product from the reaction vessel and cooling it, an amorphous polyester resin (PS1) having the following physical properties was obtained. Incidentally, since no clear endothermic peak was confirmed in the endothermic curve measured using a differential scanning calorimeter for the obtained polyester resin (PS1) and no clear melting point could be measured, it was judged to be amorphous.

[0107] (Physical properties of amorphous polyester resin (PS1)) Softening point (Tm): 100 °C Glass transition point (Tg): 50 °C Weight average molecular weight (Mw): 30,000 Acid value: 15 mgKOH / g Hydroxyl value: 30 mgKOH / g

[0108] <Preparation of toner> Toner (TA-1) to (TA-23) and (TB-1) to (TB-8) were prepared. The compositions of these toners are shown in Tables 7 to 10 described later. Note that toner (TA-1) to (TA-23) and (TB-1) to (TB-8) were used for the preparation of developer (A-1) to (A-23) and (B-1) to (B-8), respectively. For the sake of understanding, in Tables 7 to 10, toners having the same composition are also indicated by different toner numbers corresponding to the developer numbers.

[0109] (Preparation of Toner (TA-1)) Using an FM mixer ("FM-10B" manufactured by Nippon Coke & Engineering Co., Ltd.), 100 parts by mass of a binder resin, 4 parts by mass of a colorant, 1 part by mass of a charge control agent, and 5 parts by mass of a release agent were mixed to obtain a mixture. As the binder resin, the amorphous polyester resin (PS1) obtained in the above <Synthesis of Amorphous Polyester Resin (PS1)> was used. As the colorant, copper phthalocyanine blue pigment (C.I.Pigment Blue 15:3) was used. As the charge control agent, a quaternary ammonium salt ("BONTRON (registered trademark) P-51" manufactured by Orient Chemical Industries, Ltd.) was used. As the release agent, carnauba wax ("Special Carnauba Wax No. 1" manufactured by Kato Yoko Co., Ltd.) was used. The obtained mixture was melt-kneaded using a twin-screw extruder ("PCM-30 type" manufactured by Ikegai Corporation) to obtain a melt-kneaded product. The melt-kneaded product was pulverized using a mechanical pulverizer ("Turbo Mill" manufactured by Freund Turbo Co., Ltd.) to obtain a pulverized product. The pulverized product was classified using a classifier ("Elbow Jet" manufactured by Nippon Steel Mining Co., Ltd.). Thereby, powdery toner mother particles having a volume median diameter of 6.8 μm were obtained.

[0110] 100.0 parts by mass of toner mother particles, 1.5 parts by mass of small-diameter silica particles, and 0.4 parts by mass of large-diameter silica particles (S1) were mixed using an FM mixer ("FM-10B" manufactured by Nippon Coke & Engineering Co., Ltd.) under the condition of 4,000 rpm for 5 minutes. The obtained mixture was sieved using a 200-mesh (aperture 75 μm) sieve to obtain toner (TA-1).

[0111] (Preparation of Toners (TA-2) to (TA-23) and (TB-1) to (TB-8)) Toners (TA-2) to (TA-23) and (TB-1) to (TB-8) were each prepared in the same manner as the preparation of toner (TA-1), except that the large-diameter silica particles of the types shown in Tables 7 to 10 were used in the amounts shown in Tables 7 to 10.

[0112] <Preparation of Developer Using a shaker mixer ("Turbular (registered trademark) Mixer T2F" manufactured by Willy E. Bachofen (WAB)), 6 parts by mass of toner and 100 parts by mass of carrier were mixed for 30 minutes to obtain a developer with a toner concentration of 6% by mass. For the preparation of the developer, the toners and carriers shown in Tables 7 to 10 were used. For example, for the preparation of developer (A-1), toner (TA-1) and carrier (CA-1) shown in the "Developer (A-1)" column of Table 7 were used.

[0113] <Measurement of Saturated Magnetization The saturated magnetization of the carrier core was measured using a high-sensitivity vibrating sample type magnetometer ("VSM-P7" manufactured by Toei Industry Co., Ltd.) under the condition of an external magnetic field of 3000 (unit: Oe). The measurement results are shown in Tables 3 to 6.

[0114] <Measurement of Volume Median Diameter The volume median diameter of the carrier core was measured using a laser diffraction / scattering particle size distribution measuring device ("LA-950" manufactured by Horiba, Ltd.). The measurement results are shown in Tables 3 to 6.

[0115] <Measurement of Number-Average Primary Particle Diameter The number-average primary particle diameters of barium titanate particles, small-diameter silica particles, and large-diameter silica particles were measured using a scanning electron microscope (field emission scanning electron microscope, "JSM-7600F" manufactured by JEOL Ltd.). In the measurement of the number-average primary particle diameter, the equivalent circle diameters (Heywood diameters: the diameters of circles having the same area as the projected area of the primary particles) of 100 primary particles were measured, and the number-average value thereof was determined. The measurement results of the number-average primary particle diameters of the barium titanate particles are shown in Tables 3 to 6. The measurement results of the number-average primary particle diameters of the small-diameter silica particles and the large-diameter silica particles are shown in Tables 7 to 10.

[0116] <Measurement of Coating Rate> (Taking a Reflection Electron Image of the Surface of Carrier Particles) A conductive tape was fixed to the SEM sample stage with the adhesive surface facing upward. Carrier particles of the carrier were scattered on the adhesive surface of this conductive tape. Next, excess carrier particles were removed from the adhesive surface by air blowing. Next, a medicine wrapping paper was placed over the adhesive surface, and the carrier particles were fixed to the conductive tape by applying a load to the carrier particles through the medicine wrapping paper. Next, the medicine wrapping paper was peeled off from the adhesive surface of the conductive tape. Thereby, a sample including the conductive tape and the carrier particles dispersed and fixed on the adhesive surface of the conductive tape was obtained. Using a field emission scanning electron microscope (FE-SEM, "JSM-7600F" manufactured by JEOL Ltd.), a reflection electron image (surface photographed image) of the surface of the carrier particles of the obtained sample was taken. The setting conditions of the FE-SEM were as follows.

[0117] (FE-SEM Setting Conditions for Coating Rate Measurement) ·Acceleration voltage of electron beam during photography: 1 kV ·Measurement mode: BE mode (mode mainly detecting signals of reflected electrons) ·Magnification: 500 times ·Emission current: 10 μA ·Irradiation current: 450 pA ·Photography mode: Integration integration (256 times)

[0118] (Image Analysis) The obtained image (surface photograph of carrier particles) was analyzed using image analysis software ("WinROOF" manufactured by Mitani Shoko Co., Ltd.). Specifically, first, a histogram with the number of pixels on the vertical axis and luminance on the horizontal axis was created from the image. The created histogram included a low-luminance peak P corresponding to the conductive tape in the image BG1 and a medium-luminance peak P corresponding to the coating layer in the image CL1 and a high-luminance peak P corresponding to the carrier core in the image CC1 . Next, the image was binarized using the luminance at the minimum value between peak P BG1 and peak P CL1 as the threshold. As a result, the image was divided into the area of the conductive tape and the area combining the coated area and the non-coated area. The coated area corresponded to the area indicated by the medium-luminance peak P CL1 derived from the coating layer. The non-coated area corresponded to the area indicated by the high-luminance peak P CC1 derived from the carrier core exposed without being coated by the coating layer. Next, by performing area calculation based on the binarized image, the total area (A CL1 +A CC1 ) of the coated area and the non-coated area in the image was calculated. Next, the binarization conditions were changed, and the luminance at the minimum value between peak P CL1 and peak P CC1 was set as the threshold. As a result, the area combining the coated area and the non-coated area was divided into the non-coated area and the coated area. Then, the area (A CC1 ) of the non-coated area and the area (A CL1 ) of the coated area were calculated. Next, based on the measured values, the formula "Coating rate = 100 × Area of the coated area (A CL1 ) / Area of the surface of the carrier core = 100 × Area of the coated area (A CL1 ) / Total area of the coated area and the non-coated area (A CL1 +A CC1)」, the coverage rate of the carrier core was determined for the surface image of one carrier particle. For each of the surface images of 100 carrier particles, the carrier core coverage rate was determined. From the coverage rates of 100 carrier cores, the coverage rate of the carrier core (the number average value of the coverage rates) was determined. The coverage rate of the carrier core is shown in Tables 3 to 6.

[0119] <Measurement of BET Specific Surface Area> Using an automatic specific surface area measuring device ("Macsorb model 1208" manufactured by Mountech Co., Ltd.), nitrogen was adsorbed on the surface of the sample (each carrier), and the BET specific surface area of the sample was measured by the flow method (BET one-point method). Specifically, the mass of the empty cell was measured. Next, 9 g of the sample was filled into the cell so as not to adhere to the inner wall surface of the cell. While adjusting the flow rate of nitrogen to 25 mL / min using a flow meter, nitrogen was passed through the cell filled with the sample at a temperature of 45 °C for 30 minutes. In this way, the degassing of the sample was performed. Then, after cooling the cell for 2 minutes, the measurement was started using an automatic specific surface area measuring device. After the start of the measurement, the cell was immersed in the liquid nitrogen in the Dewar flask to perform the adsorption process, and then the cell was returned from the Dewar flask to the atmosphere to perform the desorption process. The actual surface area of the sample was measured by automatic measurement during the desorption process. Based on the measured value, from the formula "specific surface area = actual surface area of the sample / mass of the sample", the BET specific surface area of the sample (unit: m 2 / g) was determined. The measurement results are shown in Tables 3 to 6.

[0120] <Measurement of Shape Factor> First, the volume median diameter of the carrier particles was measured using a laser diffraction / scattering particle size distribution measuring device ("LA-950" manufactured by Horiba, Ltd.), and the measured value was taken as the actually measured carrier particle diameter (unit: μm).

[0121] Next, the true specific gravity of the carrier particles (unit: g / cm 3) was measured using a dry-type automatic densitometer (Microtrac Inc.'s "AccuPyc II 1340 series", accessory: multi-volume kit, measurement principle: dry density measurement by constant volume expansion method). From the measured true specific gravity of the carrier particles and the BET specific surface area of the carrier particles measured in the above <Measurement of BET Specific Surface Area>, the calculated carrier particle diameter (unit: μm) was obtained according to the formula "Calculated carrier particle diameter = 6 / (true specific gravity of carrier particles × BET specific surface area of carrier particles)".

[0122] Next, the shape factor of the carrier particles was obtained from the formula "Shape factor of carrier particles = Measured carrier particle diameter / Calculated carrier particle diameter". The obtained shape factor of the carrier particles is shown in Tables 3 to 6.

[0123] <Calculation of Ratio (Coating Rate / Shape Factor)> Based on the coating rate of the carrier core measured in the above <Measurement of Coating Rate> and the shape factor of the carrier particles measured in the above <Measurement of Shape Factor>, the ratio (coating rate / shape factor) was obtained according to the formula "Ratio (coating rate / shape factor) = Coating rate of carrier core / Shape factor of carrier particles". The obtained ratio (coating rate / shape factor) is shown in Tables 3 to 6.

[0124] <Evaluation> For the evaluation of each developer, an evaluation machine (a prototype machine manufactured by Kyocera Document Solutions Inc.) having the following configuration was used. The developer was put into the cyan developing device of the evaluation machine, and the replenishing toner was put into the cyan toner container.

[0125] (Configuration of Evaluation Machine) · Paper conveyance speed: 55 sheets / min · Surface shape of developer carrier: Knurled shape · Outer diameter of developer carrier: 20 mm in diameter · Recesses of developer carrier: 80 rows of recesses in the circumferential direction · Regulation blade: Magnetic blade made of SUS430 · Thickness of regulation blade: 1.5 mm · Conveyance amount of developer: 345 g / m 2 · Developing roller peripheral speed / drum peripheral speed: 1.8 (trail at the opposing position) · Distance between the photoreceptor and the developing roller: 0.375 mm · Photoreceptor: Amorphous silicon photoreceptor · Bias applied to the developing roller: Alternating current bias, duty 50%, rectangular wave, Vpp 1125 v, frequency 10 KHz · Charging polarity of the toner: Positive charging property

[0126] Using an evaluation machine, durability printing was carried out to print A4-sized images on 100,000 sheets of paper under the printing conditions shown in Table 11 (more specifically, conditions of the printing environment, printing mode, and printing rate of the image).

[0127] The printing environments shown in Table 11 were as follows. · LL environment: Environment with a temperature of 10°C and a relative humidity of 15% RH · NN environment: Environment with a temperature of 22°C and a relative humidity of 50% RH · HH environment: Environment with a temperature of 32.5°C and a relative humidity of 80% RH

[0128] The printing modes shown in Table 11 were as follows. · Continuous mode: A mode in which printing is continuously performed on paper · 5-sheet intermittent mode: A mode in which a printing pattern of printing on 5 sheets of paper and stopping printing for 12 seconds is repeated

[0129] The images with the printing rates shown in Table 11 were as follows. · 2%: Character image with a printing rate of 2% · 5%: Character image with a printing rate of 5% · 20%: Band image with a printing rate of 20% · 50%: Band image with a printing rate of 50%

[0130] Note that "Start" in Table 11 indicates from which sheet among 100,000 sheets the printing under the corresponding printing conditions starts. Also, "Timing of Image Evaluation" indicates at which sheet among 100,000 sheets the image evaluation is performed when the printing is completed. When changing the printing environment, after leaving the evaluation machine stationary for 24 hours in the changed printing environment, the durable printing was restarted. The evaluation results of each developer are shown in Tables 7 to 10.

[0131] (Method for Evaluating Image Density) First, in the NN environment, a solid image (A4 size) was printed on one sheet of paper using an evaluation machine, and the printed paper was used as the first evaluation paper. Next, the above-mentioned durable printing was performed. During the durable printing, at the timing of image evaluation shown in Table 11, a solid image (A4 size) was printed on one sheet of paper using an evaluation machine, and the printed paper was used as the second evaluation paper. Using a reflection densitometer ("RD-19I" manufactured by X-Rite), the image density of the solid images printed on the first evaluation paper and the second evaluation paper was measured. Then, the decrease width of the image density was calculated from the formula "Decrease width of image density = Image density of the solid image printed on the first evaluation paper - Image density of the solid image printed on the second evaluation paper". The decrease width of the image density was calculated for all the second evaluation papers, and the maximum value among the calculated decrease widths of the image density was used as the evaluation value. The evaluation value was evaluated according to the following criteria. The smaller the decrease width of the image density, the more stably an image with the desired image density can be formed. When the evaluation was A, B, and C, it was determined as qualified, and when the evaluation was D, it was determined as unqualified.

[0132] (Evaluation Criteria for Image Density) A: The decrease width of the image density is less than 0.2. B: The decrease width of the image density is 0.2 or more and less than 0.3. C: The decrease width of the image density is 0.3 or more and less than 0.4. D (Defective): The decrease width of the image density is 0.4 or more.

[0133] (Method for Evaluating Anti-Fogging Property) The above-mentioned durable printing was performed. During the durable printing, at the timing of image evaluation shown in Table 11, a blank paper image (A4 size) was printed on one sheet of paper using an evaluation machine, and the printed paper was used as the evaluation paper. The reflection density of the blank part of the evaluation paper was measured using a white light reflectometer (「TC-6DS」manufactured by Tokyo Denshoku Co., Ltd.). Then, the fog density was calculated based on the formula "fog density = reflection density of the blank part - reflection density of the unprinted paper". The fog density was calculated for all the evaluation papers, and the maximum value among the calculated fog densities was taken as the evaluation value. The evaluation value was evaluated according to the following criteria. When the evaluation was A or B, it was determined as qualified, and when the evaluation was C, it was determined as unqualified.

[0134] (Evaluation Criteria for Resistance to Fogging) A: The fog density is less than 0.010. B: The fog density is 0.010 or more and less than 0.020. C (defective): The fog density is 0.020 or more.

[0135] (Evaluation Method for Suppressing the Occurrence of Carrier Development) The above-mentioned durable printing was performed. During the durable printing, at the timing of image evaluation shown in Table 11, a blank paper image (A4 size) was printed on one sheet of paper using an evaluation machine, and the printed paper was used as the evaluation paper. A loupe with a magnification of 25 times was used to observe the blank paper image printed on the evaluation paper. The number of carriers existing in the area with an area of 10 cm 2 in the blank paper image was counted. For the blank paper image printed on one sheet of evaluation paper, the number of carriers existing in each of the 10 areas (specifically, 3 areas on the upstream side, 4 areas near the center, and 3 areas on the downstream side in the paper feed direction) was counted. Then, from the formula "number of carrier developments = total number of carriers existing in 10 areas / total area of 10 areas = total number of carriers existing in 10 areas / 100", the number of carrier developments (unit: pieces / cm 2 ) was obtained. The number of carrier developments was calculated for all the evaluation papers, and the maximum value among the calculated number of carrier developments was taken as the evaluation value. The evaluation value was evaluated according to the following criteria. When the evaluation was A, B, or C, it was determined as qualified, and when the evaluation was D, it was determined as unqualified.

[0136] (Evaluation Criteria for Suppressing the Generation of Carrier Development) A: The number of carrier developments is less than 0.1 per cm. 2 Less than. B: The number of carrier developments is 0.1 or more and less than 0.3 per cm. 2 0.1 or more and less than 2 0.3 per cm. C: The number of carrier developments is 0.3 or more and less than 1.0 per cm. 2 0.3 or more and less than 2 1.0 per cm. D (Defective): The number of carrier developments is 1.0 or more per cm. 2 1.0 or more.

[0137] (Evaluation Method for Suppressing the Deterioration of Image Quality) First, in the NN environment, using an evaluation machine, a halftone image (a band image with a printing rate of 50%) was printed on one sheet of paper, and the printed paper was used as the first evaluation paper. Next, the above-mentioned durable printing was performed. During the durable printing, at the timing of image evaluation shown in Table 11, a halftone image (a band image with a printing rate of 50%) was printed on one sheet of paper using an evaluation machine, and the printed paper was used as the second evaluation paper. The image quality of the halftone images printed on the first evaluation paper and the second evaluation paper was observed with the naked eye. Then, it was confirmed how much the image quality of the halftone image printed on the second evaluation paper had deteriorated compared to the image quality of the halftone image printed on the first evaluation paper. Among all the second evaluation papers, the evaluation paper with the most deteriorated image quality of the halftone image was evaluated according to the following criteria. When the evaluation was A, B, or C, it was determined as qualified, and when the evaluation was D, it was determined as unqualified.

[0138] (Evaluation Criteria for Suppressing the Deterioration of Image Quality) A: There is no deterioration of image quality at all. B: Slight deterioration of image quality has occurred. C: Deterioration of image quality has occurred, but the deterioration is at a level that does not cause problems in actual use. D (Defective): Deterioration of image quality has occurred, and the deterioration is obvious to the extent that it causes problems in actual use.

[0139] (Evaluation Method for Suppressing Generation of Image Defects Caused by Cleaning Defects) The above-mentioned durable printing was performed. During the durable printing, at the timing of image evaluation shown in Table 11, a character image with a printing rate of 5% was printed on one sheet of paper using an evaluation machine, and the printed paper was used as an evaluation paper. The character image printed on the evaluation paper was observed with the naked eye to confirm the presence or absence of image defects caused by cleaning defects. Note that the image defects caused by cleaning defects are image defects in which thin streaks parallel to the paper feed direction of the paper occur. Among all the evaluation papers, the evaluation paper on which the image defects caused by cleaning defects occurred most frequently was evaluated according to the following criteria. When the evaluations were A, B, and C, it was determined as qualified, and when the evaluation was D, it was determined as unqualified.

[0140] (Evaluation Criteria for Suppressing Generation of Image Defects Caused by Cleaning Defects) A: No image defects caused by cleaning defects occurred at all. B: Some image defects caused by cleaning defects occurred. C: Image defects caused by cleaning defects occurred, but the image defects were at a level that did not cause problems in actual use. D (defective): Image defects caused by cleaning defects occurred, and the image defects were prominent to the extent that there were problems in actual use.

[0141] Next, the meanings of the terms used in Tables 3 to 10 below will be explained. The meanings of the terms in Tables 3 to 10 are as follows. · Core: Carrier core · D 50 : Volume median diameter · Solid content: Solid content of the coating resin. The solid content of the coating resin is calculated by the formula "[Solid content of the coating resin (unit: part by mass)] = [Amount of silicone resin solution (unit: part by mass)] × [Solid content concentration of the silicone resin solution (unit: mass%)] / 100". ·Resin / Core: Resin / Core ratio (unit: mass%). The resin / core ratio is calculated from the formula "[Resin / Core ratio (unit: mass%)] = 100 × [mass of coating resin (unit: parts by mass)] / [mass of carrier core (unit: parts by mass)] = 100 × [solid content of silicone resin solution (unit: parts by mass)] / [mass of carrier core (unit: parts by mass)]". ·wt%: Mass % ·Parts: Parts by mass ·BT: Barium titanate particles ·Production method: Method for producing barium titanate particles ·Hydrothermal: Hydrothermal synthesis method ·Oxalate: Oxalate method ·Quantity ratio: Content of barium titanate particles relative to 100 parts by mass of coating resin ·Diameter: Number-average primary particle diameter ·CB: Carbon black particles ·Coat layer / Core: Coat layer / Core ratio. The coat layer / core ratio is calculated from the formula "[Coat layer / Core ratio (unit: mass%)] = 100 × [mass of coat layer (unit: parts by mass)] / [mass of carrier core (unit: parts by mass)] = 100 × [mass of solid content of coating solution (unit: parts by mass)] / [mass of carrier core (unit: parts by mass)] = 100 × {[solid content of silicone resin solution (unit: parts by mass)] + [mass of barium titanate (unit: parts by mass)] + [mass of carbon black (unit: parts by mass)]} / [mass of carrier core (unit: parts by mass)]". ·Coating rate: Coating rate of carrier core ·BET: BET specific surface area of carrier particles ·Coefficient: Shape coefficient of carrier particles ·Coating rate / Coefficient: Ratio (coating rate / shape coefficient) ·KR-255: Silicone resin solution ("KR-255" manufactured by Shin-Etsu Chemical Co., Ltd., solid content: methylphenyl silicone resin, solid content concentration: 50 mass%) ·KR-301: Silicone resin solution ("KR-301" manufactured by Shin-Etsu Chemical Co., Ltd., solid content: methylphenyl silicone resin, solid content concentration: 40 mass%) · ES-1001N: Silicone resin solution ("ES-1001N" manufactured by Shin-Etsu Chemical Co., Ltd., solid content: epoxy resin-modified silicone resin, solid content concentration: 45% by mass) · EC: Carbon black ("Ketjenblack EC-300J" manufactured by Lion Specialty Chemicals Co., Ltd., conductive carbon black, DBP oil absorption: 360 cm 3 / 100 g, BET specific surface area: 1270 m 2 / g, number average primary particle diameter: 39.5 nm) · MA: Carbon black ("Mitsubishi (registered trademark) Carbon Black MA100" manufactured by Mitsubishi Chemical Corporation, DBP oil absorption: 100 cm 3 / 100 g, BET specific surface area: 110 m 2 / g, number average primary particle diameter: 24 nm) · Small-diameter silica: Small-diameter silica particles · Large-diameter silica: Large-diameter silica particles · FD: Fog density · Fog: Evaluation of fog resistance · Carrier development: Evaluation of suppression of carrier development · Graininess: Evaluation of suppression of graininess reduction · Image density: Evaluation of image density · Cleaning: Evaluation of suppression of image defects caused by cleaning defects · -: Not containing the corresponding component

[0142]

Table 3

[0143]

Table 4

[0144]

Table 5

[0145]

Table 6

[0146]

Table 7

[0147]

Table 8

[0148]

Table 9

[0149]

Table 10

[0150]

Table 11

[0151] As shown in Table 5, the content of barium titanate particles in the carrier particles contained in the carrier (CB-1) of the developer (B-1) was less than 5 parts by mass with respect to 100 parts by mass of the coating resin. As shown in Table 9, both the evaluation result of the fog resistance and the evaluation result of the image density of the developer (B-1) were poor and were judged as non-conforming.

[0152] As shown in Table 5, the content of barium titanate particles in the carrier particles contained in the carrier (CB-2) of the developer (B-2) exceeded 45 parts by mass with respect to 100 parts by mass of the coating resin. As shown in Table 9, the evaluation result of the fog resistance of the developer (B-2) was poor and was judged as non-conforming.

[0153] As shown in Table 5, the number-average primary particle diameter of the barium titanate particles of the carrier particles included in the carrier (CB-3) of the developer (B-3) was less than 100 nm. As shown in Table 9, both the evaluation result of the fog resistance and the evaluation result of the image density of the developer (B-3) were poor and were judged as non-conforming.

[0154] As shown in Table 5, the number-average primary particle diameter of the barium titanate particles of the carrier particles included in the carrier (CB-4) of the developer (B-4) exceeded 500 nm. As shown in Table 9, the evaluation result of suppressing the occurrence of image defects due to cleaning defects of the developer (B-4) was poor and was judged as non-conforming.

[0155] As shown in Table 10, the external additive particles of the toner particles included in the toner (TB-5) of the developer (B-5) did not contain large-diameter silica particles. The external additive particles of the toner particles included in the toner (TB-5) contained small-diameter silica particles, but the number-average primary particle diameter of the small-diameter silica particles was less than 30 nm. As shown in Table 10, the evaluation result of the fog resistance of the developer (B-5) was poor and was judged as non-conforming.

[0156] As shown in Table 6, the coat layer / core ratio of the carrier particles included in the carrier (CB-6) of the developer (B-6) exceeded 4.90% by mass, and the coating rate of the carrier core was 100.0%. As shown in Table 10, the evaluation result of the fog resistance of the developer (B-6) was poor and was judged as non-conforming.

[0157] As shown in Table 6, the coat layer / core ratio of the carrier particles included in the carrier (CB-7) of the developer (B-7) was less than 0.09% by mass, and the coating rate of the carrier core was less than 80.0%. As shown in Table 10, both the evaluation result of the fog resistance and the evaluation result of suppressing the occurrence of carrier development of the developer (B-7) were poor and were judged as non-conforming.

[0158] As shown in Table 10, the external additive particles of the toner (TB-8) contained in the developer (B-8) included small-diameter silica particles and extra-large-diameter silica particles (S6). The number-average primary particle diameter of the small-diameter silica particles was less than 30 nm. The number-average primary particle diameter of the extra-large-diameter silica particles (S6) exceeded 120 nm. As shown in Table 10, both the evaluation result of the anti-fogging property and the evaluation result of the image density of the developer (B-8) were poor and were judged as non-conforming.

[0159] As shown in Tables 3 to 10, the developers (A-1) to (A-23) had the following compositions. That is, the external additive particles of the toner particles included large-diameter silica particles. The coating layer of the carrier particles included a coating resin and barium titanate particles, and the coating resin included a silicone resin. The number-average primary particle diameter of the barium titanate particles was 100 nm or more and 500 nm or less. The content of the barium titanate particles was 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coating resin. The coating layer / core ratio was 0.09% by mass or more and 4.90% by mass or less. The coating rate of the carrier core was 80.0% or more and less than 100.0%. As shown in Tables 7 to 10, the evaluation results of the anti-fogging property, the evaluation results of the image density, the evaluation results of suppressing the occurrence of carrier development, and the evaluation results of suppressing the occurrence of image defects due to cleaning defects of the developers (A-1) to (A-23) were all judged as conforming. Also, as shown in Tables 7 to 10, in addition to these evaluation results, the evaluation results of suppressing the reduction of the image graininess of the developers (A-1) to (A-23) were also judged as conforming.

[0160] From the above, it was shown that the developer of the present invention including the developers (A-1) to (A-23) was excellent in anti-fogging property, could stably form an image with a desired image density, could suppress the occurrence of carrier development, and was less likely to cause image defects due to cleaning defects.

Industrial Applicability

[0161] The developer according to the present invention can be used, for example, to form an image in a copying machine, a printer, or a multifunction machine.

Claims

1. A toner containing toner particles and a carrier containing carrier particles, wherein the toner particles have toner mother particles and external additive particles provided on the surface of the toner mother particles, the external additive particles include silica particles, the number average primary particle diameter of the silica particles is 30 nm or more and 120 nm or less, the carrier particles have a carrier core and a coat layer covering the surface of the carrier core, the coat layer includes a coat resin, barium titanate particles, and carbon black particles, the coat resin includes a silicone resin, the number average primary particle diameter of the barium titanate particles is 100 nm or more and 500 nm or less, the content of the barium titanate particles is 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coat resin, the content of the carbon black particles is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the coat resin, the ratio of the mass of the coat layer to the mass of the carrier core is 0.09% by mass or more and 4.90% by mass or less, the coating rate of the carrier core is 80.0% or more and less than 100.0%, and the coating rate is the ratio of the area of the coated region covered by the coat layer to the area of the surface of the carrier core, a two-component developer.

2. The ratio of the coating rate to the shape factor of the carrier particles is 1.9 or more and 11.5 or less, the two-component developer according to Claim 1.

3. The content of the barium titanate particles is 25 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coat resin, the two-component developer according to Claim 1.

4. The saturation magnetization of the carrier core is 65 emu / g or more and 90 emu / g or less, the two-component developer according to Claim 1.

5. The volume median diameter of the carrier core is 20.0 μm or more and 60.0 μm or less, the two-component developer according to Claim 1.

6. The toner mother particles contain at least one selected from the group consisting of a binder resin, a colorant, a charge control agent, and a release agent, and do not contain a nonionic surfactant, the two-component developer according to Claim 1.

7. The ratio of the mass of the coat resin to the mass of the carrier core is 0.05% by mass or more and 4.00% by mass or less, the two-component developer according to Claim 1.

8. The BET specific surface area of the carrier particles is 0.3 m 2 / g or more and 3.0 m 2 / g or less. The two-component developer according to claim 1.

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