Electrostatic charge image developing carrier, electrostatic charge image developer, process cartridge, image forming method, and image forming apparatus

Abstract

An electrostatic charge image developing carrier, an electrostatic charge image developer, a process cartridge, an image forming method, and an image forming apparatus, the electrostatic charge image developing carrier having magnetic particles and a resin coating layer on the surfaces of the magnetic particles, having inorganic particles on the surfaces or containing the inorganic particles in the resin coating layer, the inorganic particles contain Ti and any one of Ca, Sr and Ba, the average circularity of primary particles of the inorganic particles is 0.82-0.94 (inclusive), and the BET specific surface area of the magnetic particles is 0.12-0.24 m2 / g (inclusive).

Description

Technical Field

[0001] The present invention relates to a carrier for electrostatic image development, an electrostatic image developer, a processing cartridge, an image forming method, and an image forming apparatus. Background Art

[0002] As a carrier for electrostatic image development, a resin-coated carrier having a resin coating layer on the surface of magnetic particles is known. As the resin-coated carrier or a developer containing the resin-coated carrier, for example, the following is disclosed.

[0003] Patent Document 1 discloses a developer having a toner and a carrier, the toner containing inorganic particles having particles containing Si on the surface, the number average circular equivalent diameter of the particles containing Si being 5 nm or more and 15 nm or less, the surface of the core particles of the carrier being coated with a resin-containing coating layer, the volume average particle diameter being 45 μm or more and 70 μm or less, and the bulk density being 2.10 g / cm 3 or more and 2.50 g / cm 3 or less.

[0004] Patent Document 2 discloses a magnetic carrier having: magnetic carrier particles having a magnetic carrier core particle and a resin coating layer formed on the surface of the magnetic carrier core particle; and inorganic fine particles A present on the surface of the magnetic carrier particles. The magnetic carrier is characterized in that the inorganic fine particles A have a rectangular parallelepiped particle shape, the number average particle diameter (D1) of the inorganic fine particles A is 10 nm to 60 nm, the inorganic fine particles A are surface-treated with a surface treatment agent, and the solubility parameter (SP1) (J / mol) of the resin coating layer 1 / 2 and the solubility parameter (SP2) (J / mol) of the surface treatment agent 1 / 2 satisfy formula (1), and on the surface of the magnetic carrier, the coating rate of the inorganic fine particles A measured by X-ray photoelectron spectroscopy (ESCA) is 5.0 atom% to 20.0 atom%.

[0005] SP1 - SP2 ≤ 14.00......(1)

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-71669

[0007] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2020-91471 Summary of the Invention

[0008] An object of the present invention is to provide a carrier for electrostatic image development, wherein the inorganic particles are titanium dioxide, or the average roundness of the primary particles of the inorganic particles is less than 0.82 or more than 0.94, or the BET specific surface area of the magnetic particles is less than 0.12 m2 / g or more than 0.24 m 2 Compared with the case of / g, the line concentration and white spotting suppression in the obtained image are excellent.

[0009] The solution for solving the above problem includes the following methods.

[0010] <1>

[0011] A carrier for electrostatic image development, which has magnetic particles and a resin coating layer on the surface of the magnetic particles, has inorganic particles on the surface or contains inorganic particles in the resin coating layer, the inorganic particles contain Ti and any one of Ca, Sr, and Ba, the average roundness of the primary particles of the inorganic particles is 0.82 or more and 0.94 or less, and the BET specific surface area of the magnetic particles is 0.12 m 2 / g or more and 0.24 m 2 / g or less.

[0012] <2>

[0013] The carrier for electrostatic image development according to <1>, wherein

[0014] The roundness of the inorganic particles at 84% cumulative exceeds 0.92.

[0015] <3>

[0016] The carrier for electrostatic image development according to <1> or <2>, wherein

[0017] The ratio Mx / Mt of the total molar amount Mx of Ca, Sr, and Ba to the molar amount Mt of Ti in the inorganic particles is 0.65 or more and 0.90 or less.

[0018] <4>

[0019] The carrier for electrostatic image development according to any one of <1> to <3>, wherein

[0020] The fluidity of the carrier for electrostatic image development is 26 or more and 34 or less.

[0021] <5>

[0022] The carrier for electrostatic image development according to any one of <1> to <4>, wherein

[0023] The resin coating layer contains an acrylic resin having an aliphatic cyclic structure and an amino group.

[0024] <6>

[0025] The carrier for electrostatic image development according to <5>, wherein

[0026] The resin coating layer contains an acrylic resin having a structural unit with an aliphatic cyclic structure and a structural unit with an amino group.

[0027] <7>

[0028] The electrostatic image developing carrier according to any one of <1> to <6>, wherein

[0029] The average particle diameter of the electrostatic image developing carrier is 30 μm or more and 38 μm or less.

[0030] <8>

[0031] An electrostatic image developer comprising the electrostatic image developing carrier according to any one of <1> to <7> and a toner.

[0032] <9>

[0033] A process cartridge includes a developing member that houses the electrostatic image developer according to <8>, and develops an electrostatic image formed on the surface of an image holding member into a toner image, and the process cartridge is detachably attached to an image forming apparatus.

[0034] <10>

[0035] An image forming method includes: a charging step of charging at least an image holding member; an exposure step of forming an electrostatic latent image on the surface of the image holding member; a developing step of developing the electrostatic latent image formed on the surface of the image holding member with an electrostatic image developer to form a toner image; a transfer step of transferring the toner image formed on the surface of the image holding member to the surface of a transfer target; and a fixing step of fixing the toner image, and the electrostatic image developer is the electrostatic image developer according to <8>.

[0036] <11>

[0037] An image forming apparatus includes: an image holding member; a charging member that charges the image holding member; an exposure member that exposes the charged image holding member to form an electrostatic latent image on the image holding member; a developing member that develops the electrostatic latent image with an electrostatic image developer to form a toner image; a transfer member that transfers the toner image from the image holding member to a transfer target; and a fixing member that fixes the toner image, and the electrostatic image developer is the electrostatic image developer according to <8>.

[0038] Advantages of the Invention

[0039] According to the invention related to <1>, the following developer for electrostatic image development is provided. When the inorganic particles are titanium dioxide, or the average roundness of the primary particles of the inorganic particles is less than 0.82 or more than 0.94, or the BET specific surface area of the magnetic particles is less than 0.12 m 2 / g or more than 0.24 m 2 / g, the line density and white spot suppression in the obtained image are excellent.

[0040] According to the invention related to <2>, the following developer for electrostatic image development is provided. Compared with the case where the roundness of 84% cumulative of the inorganic particles is 0.92 or less, the line density and white spot suppression in the obtained image are more excellent.

[0041] According to the invention related to <3>, the following developer for electrostatic image development is provided. Compared with the case where the ratio Mx / Mt of the total molar amount Mx of Ca, Sr, and Ba to the molar amount Mt of Ti in the inorganic particles is less than 0.65 or more than 0.90, the line density and white spot suppression in the obtained image are more excellent.

[0042] According to the invention related to <4>, the following developer for electrostatic image development is provided. Compared with the case where the fluidity is less than 26 or more than 34, the line density in the obtained image is more excellent.

[0043] According to the invention related to <5> or <6>, the following developer for electrostatic image development is provided. Compared with the case where the resin coating layer only contains an acrylic resin having an aliphatic cyclic structure and no amino group, the line density in the obtained image is more excellent.

[0044] According to the invention related to <7>, the following developer for electrostatic image development is provided. Compared with the case where the average particle size is less than 30 μm or more than 38 μm, the line density in the obtained image is more excellent.

[0045] According to the inventions related to <8> to <11>, the following electrostatic image developer, process cartridge, image forming method, or image forming apparatus is provided. When the inorganic particles in the electrostatic image developer are titanium dioxide, or the average roundness of the primary particles of the inorganic particles is less than 0.82 or more than 0.94, or the BET specific surface area of the magnetic particles is less than 0.12 m 2 / g or more than 0.24 m 2 / g, the line density and white spot suppression in the obtained image are excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The embodiments of the present invention will be described in detail with reference to the following drawings.

[0047] Figure 1It is a schematic diagram of the image used in the linear concentration and white spot inhibition evaluation;

[0048] Figure 2 It is shown in Figure 1 The schematic diagram of the evaluation part in the white spot inhibition evaluation in the shown image;

[0049] Figure 3 It is a schematic structural diagram showing an example of an image forming apparatus according to the present embodiment;

[0050] Figure 4 It is a schematic structural diagram showing an example of a process cartridge detachably attached to the image forming apparatus according to the present embodiment.

[0051] Symbol description

[0052] IM: Image, HD: High-concentration image part, LD: Low-concentration image part, R: White spot inhibition evaluation part.

[0053] 1Y, 1M, 1C, 1K - Photoconductor (an example of an image holding member), 2Y, 2M, 2C, 2K - Charging roller (an example of a charging member), 3 - Exposure device (an example of an electrostatic image forming member), 3Y, 3M, 3C, 3K - Laser beam, 4Y, 4M, 4C, 4K - Developing device (an example of a developing member), 5Y, 5M, 5C, 5K - Primary transfer roller (an example of a primary transfer member), 6Y, 6M, 6C, 6K - Photoconductor cleaning device (an example of a cleaning member), 8Y, 8M, 8C, 8K - Toner cartridge, 10Y, 10M, 10C, 10K - Image forming unit, 20 - Intermediate transfer belt (an example of an intermediate transfer member), 22 - Driving roller, 24 - Supporting roller, 26 - Secondary transfer roller (an example of a secondary transfer unit), 28 - Fixing device (an example of a fixing member), 30 - Intermediate transfer member cleaning device, P - Recording paper (an example of a recording medium); 107 - Photoconductor (an example of an image holding member), 108 - Charging roller (an example of a charging member), 109 - Exposure device (an example of an electrostatic image forming member), 111 - Developing device (an example of a developing member), 112 - Transfer device (an example of a transfer member), 113 - Photoconductor cleaning device (an example of a cleaning member), 115 - Fixing device (an example of a fixing member), 116 - Mounting rail, 117 - Housing, 118 - Opening for exposure, 200 - Process cartridge, 300 - Recording paper (an example of a recording medium). Detailed description of the specific embodiment

[0054] Hereinafter, an embodiment as an example of the present invention will be described in detail.

[0055] In this specification, when referring to the amounts of the respective components in a composition, when there are multiple substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the multiple substances present in the composition.

[0056] In this specification, the numerical range represented by "~" means a range that includes the numerical values described before and after "~" as the minimum value and the maximum value, respectively.

[0057] In this specification, the term "process" includes not only independent processes, but also those that, even if not clearly distinguishable from other processes, are included in this term as long as they can achieve the intended purpose of the process.

[0058] In this specification, the "carrier for electrostatic image development" is also referred to as "carrier", the "toner for electrostatic image development" is also referred to as "toner", and the "electrostatic image developer" is also referred to as "developer".

[0059] (Carrier for electrostatic image development)

[0060] The carrier for electrostatic image development according to this embodiment has magnetic particles and a resin coating layer on the surface of the magnetic particles, has inorganic particles on the surface or contains inorganic particles in the resin coating layer. The inorganic particles contain Ti and any one of Ca, Sr, and Ba. The average roundness of the primary particles of the inorganic particles is 0.82 or more and 0.94 or less. The BET specific surface area of the magnetic particles is 0.12 m 2 / g or more and 0.24 m 2 / g or less.

[0061] In conventional carriers, when continuously printing a fine line image at low temperature and low humidity, sometimes the line density becomes faint. Also, after continuously printing a fine line image, in a combined image with different densities such as an intermediate tone image inside a solid image, sometimes the image at the boundary part is not printed and becomes a white spot. This is because, during continuous printing of a fine line image, the charging of the toner increases and it becomes difficult to show density.

[0062] In the carrier for electrostatic image development according to this embodiment, as an external additive or at least contains inorganic particles in the resin coating layer. The inorganic particles contain Ti and any one of Ca, Sr, and Ba. The average roundness of the primary particles of the inorganic particles is 0.82 or more and 0.94 or less. The BET specific surface area of the magnetic particles is 0.12 m 2 / g or more and 0.24 m 2Below 100 μg / g, thus, if there are inorganic particles containing Ti and any one of Ca, Sr, and Ba, the dielectric properties of the inorganic particles are high and the resistance is moderately low. Therefore, the change in charge can be suppressed, and the charge can be maintained according to the dielectric properties, and the charge can be prevented from becoming too high due to the resistance.

[0063] When the BET specific surface area of the magnetic particles is within the above range, an appropriate contact point between the core and the inorganic particles can be formed. By moderately generating charge leakage from the inorganic particles to the core, electrostatic attraction and repulsion can be suppressed, and the amount present on the carrier surface can be stabilized.

[0064] Moreover, if the average roundness of the primary particles of the inorganic particles is within the above range, the accumulation of the inorganic particles on the carrier surface can be suppressed, and the mobility on the carrier surface is also appropriate.

[0065] Therefore, if the BET specific surface area and the roundness are within the above range, their effects work synergistically, the amount of inorganic particles on the carrier remains constant regardless of external conditions and the variation is suppressed, and the detachment of the inorganic particles from the carrier, which is likely to occur in continuous printing with low image density at low temperature and low humidity, can be suppressed. In particular, in printing with different image densities, effects can be obtained in terms of on-line density and image white spots.

[0066] Hereinafter, the structure of the carrier for electrostatic image development according to the present embodiment will be described in detail.

[0067] <Average roundness of primary particles of inorganic particles>

[0068] In the carrier for electrostatic image development according to the present embodiment, the average roundness of the primary particles of the inorganic particles is 0.82 or more and 0.94 or less. From the viewpoints of the line density and white spot suppression of the obtained image, it is preferably 0.85 or more and 0.94 or less, more preferably 0.88 or more and 0.93 or less, and particularly preferably 0.91 or more and 0.93 or less.

[0069] Regarding the average roundness of the inorganic particles in the present embodiment, the roundness is obtained by image analysis of at least 300 inorganic particles, a roundness distribution is made, and the average roundness is obtained by taking the average of the roundness. And the roundness of the inorganic particles corresponding to the cumulative 84% described below is obtained from the made roundness distribution. The inorganic particles refer to the particles present on the surface of the carrier after removing the toner from the electrostatic image developer using an arbitrary filter and blowing air. And regarding the inorganic particles, each element on the carrier is mapped by energy dispersive X-ray analysis (SEM-EDX) and titanium compounds, etc. are identified based on the elements of each particle on the carrier.

[0070] <BET specific surface area of magnetic particles>

[0071] In the carrier for electrostatic image development according to this embodiment, the BET specific surface area of the magnetic particles is 0.12 m 2 / g or more and 0.24 m 2 / g or less. From the viewpoints of the line density and white spot suppression property of the obtained image, for example, it is preferably 0.13 m 2 / g or more and 0.23 m 2 / g or less, more preferably 0.15 m 2 / g or more and 0.23 m 2 / g or less, and particularly preferably 0.16 m 2 / g or more and 0.22 m 2 / g or less.

[0072] The method for measuring the BET specific surface area of the magnetic particles in this embodiment is as follows.

[0073] Using an arbitrary filter screen, the toner is removed from the electrostatic image developer by blowing air. Then, the coating film is removed with a solvent to obtain magnetic particles.

[0074] The obtained magnetic particles are placed in a cell of a SA3100 specific surface area measuring device (manufactured by BECKMAN COULTER), degassed at 60 °C for 120 minutes, purged with a mixed gas of nitrogen and helium (volume ratio 30:70), and measured by the continuous one-point method.

[0075] <Inorganic particles>

[0076] The carrier for electrostatic image development according to this embodiment has magnetic particles and a resin coating layer on the surface of the magnetic particles, and has inorganic particles on the surface or contains inorganic particles in the resin coating layer. The inorganic particles contain Ti and any one of Ca, Sr, and Ba.

[0077] Inorganic particles may be provided on the surface of the carrier, or may be contained in the resin coating layer. However, from the viewpoints of the line density and white spot suppression property of the obtained image, for example, it is preferably to have inorganic particles on the surface of the carrier.

[0078] Moreover, when inorganic particles are provided on the surface of the carrier, they can be externally added to the carrier and attached to the surface, or inorganic particles in a free amount can be externally added to the toner and transferred to the carrier when producing the electrostatic image developer.

[0079] Examples of the inorganic particles include calcium titanate particles, strontium titanate particles, or barium titanate particles.

[0080] Among them, from the viewpoints of the line density and white spot suppression property of the obtained image, for example, strontium titanate particles are particularly preferably used.

[0081] Moreover, from the viewpoints of the line density and white spot suppression property of the obtained image, the inorganic particles preferably contain Ti and Sr, for example.

[0082] From the viewpoints of the line density and white spot suppression property of the obtained image, the ratio Mx / Mt of the total molar amount Mx of Ca, Sr, and Ba to the molar amount Mt of Ti in the inorganic particles is preferably 0.60 or more and 0.95 or less, more preferably 0.65 or more and 0.90 or less, and particularly preferably 0.75 or more and 0.85 or less, for example.

[0083] The method for measuring Mx / Mt in the present embodiment is as follows.

[0084] Mapping of each element on the carrier was performed by energy dispersive X-ray analysis (SEM-EDX). The titanate compound was identified based on the elements of each particle on the carrier, and the coating rate was calculated.

[0085] Moreover, the net intensity was measured by SEM-EDX, and the net intensity ratio of the particles in which Ti and Ca / Sr / Ba were synchronized was calculated.

[0086] A calibration curve was separately prepared, molar conversion was performed, the molar amounts (Mt and Mx) were obtained, and Mx / Mt was calculated.

[0087] From the viewpoints of the line density and white spot suppression property of the obtained image, the average primary particle diameter of the inorganic particles is preferably 10 nm or more and 100 nm or less, more preferably 20 nm or more and 90 nm or less, further preferably 30 nm or more and 80 nm or less, and particularly preferably 30 nm or more and 60 nm or less, for example.

[0088] In the present embodiment, the primary particle diameter of the inorganic particles means the diameter of a circle having the same area as the primary particle image (so-called circular equivalent diameter), and the average primary particle diameter of the inorganic particles means the particle diameter at which the cumulative amount becomes 50% from the smaller diameter side in the distribution based on the number of primary particle diameters. Regarding the primary particle diameter of the inorganic particles, image analysis is performed on at least 300 inorganic particles to obtain it. The inorganic particles refer to the particles present on the surface of the carrier after removing the toner from the electrostatic image developer by blowing using an arbitrary filter. Moreover, regarding the inorganic fine particles, mapping of each element on the carrier is performed by energy dispersive X-ray analysis (SEM-EDX), and the titanate compound is identified based on the elements of each particle on the carrier.

[0089] The average primary particle diameter of the inorganic particles can be controlled by various conditions when manufacturing the inorganic particles using a wet method, for example.

[0090] In this embodiment, the shape of the inorganic particles is not particularly limited. However, from the viewpoint of suppressing fogging, a shape with rounded corners is preferred rather than a cube or a rectangular parallelepiped.

[0091] The roundness of the inorganic particles at a cumulative 84% is the roundness of the primary particles at a cumulative 84%. From the viewpoints of a narrow number distribution of roundness, less uneven adhesion to the carrier, and suppression of line density and white spots in the obtained image, it is preferably more than 0.92, more preferably 0.93 or more, and particularly preferably 0.95 or more.

[0092] In addition, regarding the inorganic particles, the roundness of the primary particles at a cumulative 84% is one of the indices of a shape with rounded corners. If it is a value exceeding 0.92, it can be said to be a shape with rounded corners.

[0093] In this embodiment, the inorganic particles are preferably doped with a metal element other than titanium, calcium, strontium, and barium (hereinafter, also referred to as a dopant). By including the dopant in the inorganic particles, the crystallinity of the perovskite structure decreases and becomes a shape with rounded corners.

[0094] The dopant of the inorganic particles is not particularly limited as long as it is an element other than titanium, calcium, strontium, and barium. An element having an ionic radius that can enter the crystal structure constituting the inorganic particles when ionized is preferred. From this viewpoint, the dopant of the inorganic particles is preferably an element having an ionic radius of 40 pm or more and 200 pm or less when ionized, and more preferably 60 pm or more and 150 pm or less when ionized.

[0095] Specific examples of the dopant of the inorganic particles include lanthanide elements, silicon dioxide (silicon), aluminum, magnesium, calcium, barium, phosphorus, sulfur, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, yttrium, zinc, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, antimony, tantalum, tungsten, rhenium, osmium, iridium, platinum, bismuth, etc. As the lanthanide element, lanthanum or cerium is preferably used, for example. Among these, silicon dioxide or lanthanum is preferably used, for example, from the viewpoints of the line density and white spot suppression of the obtained image.

[0096] As a dopant for inorganic particles, from the viewpoint of not making the inorganic particles overly negatively charged, for example, an element with an electronegativity of 2.0 or less is preferred. In the present embodiment, the electronegativity is the Allred-Rochow electronegativity. Examples of elements with an electronegativity of 2.0 or less include lanthanum (electronegativity 1.08), magnesium (1.23), aluminum (1.47), silicon dioxide (1.74), calcium (1.04), vanadium (1.45), chromium (1.56), manganese (1.60), iron (1.64), cobalt (1.70), nickel (1.75), copper (1.75), zinc (1.66), gallium (1.82), yttrium (1.11), zirconium (1.22), niobium (1.23), silver (1.42), indium (1.49), tin (1.72), barium (0.97), tantalum (1.33), rhenium (1.46), cerium (1.06), etc.

[0097] Regarding the amount of the dopant in the inorganic particles, from the viewpoint of having a perovskite-type crystal structure and a rounded shape, the dopant is preferably in the range of 0.1 mol% or more and 20 mol% or less, more preferably in the range of 0.1 mol% or more and 15 mol% or less, and still more preferably in the range of 0.1 mol% or more and 10 mol% or less, relative to calcium, strontium, and barium.

[0098] In the present embodiment, from the viewpoint of improving the function of the inorganic particles, the inorganic particles are preferably, for example, inorganic particles having a hydrophobized surface. It is presumed that the hydrophobized inorganic particles repel each other on the resin-coated magnetic particles and are easily dispersed with high uniformity.

[0099] In the present embodiment, the inorganic particles are more preferably, for example, inorganic particles having a surface hydrophobized with a silicon-containing organic compound. Compared with inorganic particles hydrophobized with a treatment agent having a strong positive charge such as a fatty acid metal salt, the inorganic particles hydrophobized with a silicon-containing organic compound are less likely to migrate to the non-image portion on the photoreceptor and less likely to cause image defects.

[0100] The inorganic particles preferably have a surface containing 1 mass% or more and 50 mass% or less (for example, preferably 5 mass% or more and 40 mass% or less, more preferably 5 mass% or more and 30 mass% or less, still more preferably 10 mass% or more and 25 mass% or less) of a silicon-containing organic compound relative to their mass.

[0101] That is, the hydrophobization treatment amount based on the silicon-containing organic compound is preferably 1 mass% or more and 50 mass% or less, more preferably 5 mass% or more and 40 mass% or less, still more preferably 5 mass% or more and 30 mass% or less, and still more preferably 10 mass% or more and 25 mass% or less, relative to the mass of the inorganic particles.

[0102] When the amount of hydrophobization treatment is within the above range, fogging is easily suppressed. When the amount of hydrophobization treatment is 30% by mass or less, generation of aggregates due to the surface subjected to hydrophobization treatment is suppressed.

[0103] In the present embodiment, the water content rate of the inorganic particles is preferably, for example, 1.5% by mass or more and 10% by mass or less. When the water content rate is 1.5% by mass or more and 10% by mass or less (for example, more preferably 2% by mass or more and 5% by mass or less), the resistance of the inorganic particles is controlled within an appropriate range, and unevenness caused by electrostatic repulsion between the inorganic particles is excellently suppressed. The water content rate of the inorganic particles can be controlled, for example, by manufacturing the inorganic particles using a wet method and adjusting the temperature and time of the drying treatment. When hydrophobization treatment is performed on the inorganic particles, the water content rate of the inorganic particles can be controlled by adjusting the temperature and time of the drying treatment after the hydrophobization treatment.

[0104] The water content rate of the inorganic particles is measured as follows.

[0105] After conditioning 20 mg of the measurement sample in a chamber at a temperature of 22°C / relative humidity of 55% for 17 hours, it is heated from 30°C to 250°C at a temperature increase rate of 30°C / minute in a nitrogen atmosphere in a room at a temperature of 22°C / relative humidity of 55% using a thermogravimetric balance (TGA-50 type manufactured by Shimadzu Corporation), and the heating loss (mass lost due to heating) is measured. Based on the measured heating loss, the water content rate is calculated by the following formula.

[0106] Water content rate (% by mass) = (Heating loss under the conditions of 30°C to 250°C) ÷ (Mass before heating after conditioning) × 100

[0107] With respect to the total mass of the carrier, the content of the inorganic particles contained in the electrostatic image developing carrier according to the present embodiment is preferably, for example, 0.01% by mass or more and 0.8% by mass or less, more preferably 0.01% by mass or more and 0.5% by mass or less, still more preferably 0.02% by mass or more and 0.08% by mass or less, and still more preferably 0.04% by mass or more and 0.05% by mass or less.

[0108] The inorganic particles may be the inorganic particles themselves, or may be particles obtained by hydrophobizing the surface of the inorganic particles (sometimes referred to as mother particles). The method for manufacturing the inorganic particles (mother particles) is not particularly limited, and from the viewpoint of controlling the particle diameter and shape, a wet method is preferred.

[0109] A wet method for producing inorganic particles is, for example, a production method in which an aqueous alkali solution is added to a mixed solution of a titanium oxide source and a calcium, strontium, or barium source while reacting them, and then an acid treatment is performed. In this production method, the particle size of the inorganic particles is controlled according to the mixing ratio of the titanium oxide source and the calcium, strontium, or barium source, the concentration of the titanium oxide source at the initial stage of the reaction, the temperature and addition rate when adding the aqueous alkaline solution, and the like.

[0110] Surface treatment of the inorganic particles is performed, for example, by preparing a treatment liquid obtained by mixing a silicon-containing organic compound as a hydrophobizing agent and a solvent, mixing the inorganic particles and the treatment liquid while stirring, and further continuing stirring. After the surface treatment, a drying treatment is performed for the purpose of removing the solvent of the treatment liquid.

[0111] Examples of the silicon-containing organic compound used in the surface treatment of the inorganic particles include alkoxysilane compounds, silazane compounds, silicone oils, and the like.

[0112] Examples of the alkoxysilane compounds used in the surface treatment of the inorganic particles include tetramethoxysilane, tetraethoxysilane; methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, decyltriethoxysilane, dodecyltriethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, phenyltriethoxysilane, benzyltriethoxysilane; dimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane; trimethylmethoxysilane, trimethylethoxysilane.

[0113] Examples of the silazane compounds used in the surface treatment of the inorganic particles include dimethyldisilazane, trimethyldisilazane, tetramethyldisilazane, pentamethyldisilazane, hexamethyldisilazane, and the like.

[0114] Examples of the silicone oils used in the surface treatment of the inorganic particles include silicone oils such as dimethylpolysiloxane, diphenylpolysiloxane, benzylpolysiloxane; reactive silicone oils such as amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, methanol-modified polysiloxane, fluorine-modified polysiloxane, methacrylic acid-modified polysiloxane, mercapto-modified polysiloxane, phenol-modified polysiloxane, and the like.

[0115] As the solvent used in the preparation of the treatment liquid, when the silicon-containing organic compound is an alkoxysilane compound or a silazane compound, alcohols (e.g., methanol, ethanol, propanol, butanol) are preferred, for example. When the silicon-containing organic compound is a silicone oil, hydrocarbons (e.g., benzene, toluene, n-hexane, n-heptane) are preferred, for example.

[0116] In the treatment liquid, the concentration of the silicon-containing organic compound is preferably, for example, 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and still more preferably 10% by mass or more and 30% by mass or less.

[0117] With respect to 100 parts by mass of the inorganic particles, the amount of the silicon-containing organic compound used in the surface treatment is preferably, for example, 1 part by mass or more and 50 parts by mass or less, more preferably 5 parts by mass or more and 40 parts by mass or less, and still more preferably 5 parts by mass or more and 30 parts by mass or less.

[0118] <Magnetic particles>

[0119] The magnetic particles are not particularly limited, and known magnetic particles used as the core material of the carrier can be applied. As the magnetic particles, specifically, particles of magnetic metals such as iron, nickel, and cobalt; particles of magnetic oxides such as ferrite and magnetite; resin-impregnated magnetic particles obtained by impregnating a porous magnetic powder with a resin; magnetic powder-dispersed resin particles obtained by dispersing and blending a magnetic powder in a resin, etc. can be cited.

[0120] In the present embodiment, as the magnetic particles, ferrite particles are preferred, for example.

[0121] In the present embodiment, the ferrite particles preferably contain at least one selected from calcium oxide and strontium oxide, for example. Calcium oxide and strontium oxide are easily contained in the surface of the ferrite particles. It is presumed that if calcium or strontium elements are present on the surface of the ferrite particles, the charge leakage from the ferrite particles is suppressed, and the surface of the carrier is relatively highly charged. According to this carrier, the low charging of the toner in the developing device is suppressed, and as a result, fogging is further suppressed, and furthermore, the fine line reproducibility is improved (e.g., suppression of thickening, collapse, or blurring of the fine line). This effect is remarkable when forming an image with a low density of the same color after repeatedly performing high-concentration and high-density monochromatic image formation at a higher speed.

[0122] In the present embodiment, the ferrite particles contain, for example, at least one selected from calcium oxide and strontium oxide, and the total content of calcium element and strontium element is preferably 0.1% by mass or more and 2.0% by mass or less with respect to the total mass of the ferrite particles. If the total content of calcium element and strontium element is 0.1% by mass or more with respect to the total mass of the ferrite particles, charge leakage from the ferrite particles is effectively suppressed. If the total content of calcium element and strontium element is 2.0% by mass or less with respect to the total mass of the ferrite particles, the crystal structure of the ferrite particles is regular, and the resistance value and magnetic susceptibility are within appropriate ranges. As a result, fogging is further suppressed, and furthermore, the reproduction of fine lines is improved (for example, suppression of thickening, collapse, or blurring of fine lines).

[0123] From the above viewpoints, with respect to the total ferrite particles, the total content of calcium element and strontium element is preferably, for example, 0.1% by mass or more and 2.0% by mass or less, more preferably 0.2% by mass or more and 1.5% by mass or less, and still more preferably 0.5% by mass or more and 1.2% by mass or less.

[0124] In the present embodiment, the ferrite particles contain, for example, calcium oxide, and the content of calcium element is preferably 0.2% by mass or more and 2.0% by mass or less with respect to the total mass of the ferrite particles. If the content of calcium element is 0.2% by mass or more with respect to the total mass of the ferrite particles, charge leakage from the ferrite particles is effectively suppressed. If the content of calcium element is 2.0% by mass or less with respect to the total mass of the ferrite particles, the crystal structure of the ferrite particles is regular, and the resistance value and magnetic susceptibility are within appropriate ranges. As a result, fogging is further suppressed, and furthermore, the reproduction of fine lines is improved (for example, suppression of thickening, collapse, or blurring of fine lines).

[0125] From the above viewpoints, with respect to the total ferrite particles, the content of calcium element is preferably, for example, 0.2% by mass or more and 2.0% by mass or less, more preferably 0.5% by mass or more and 1.5% by mass or less, and still more preferably 0.5% by mass or more and 1.0% by mass or less.

[0126] In the present embodiment, the ferrite particles contain, for example, strontium oxide, and the content of strontium element is preferably 0.1% by mass or more and 1.0% by mass or less with respect to the total mass of the ferrite particles. If the content of strontium element is 0.1% by mass or more with respect to the total mass of the ferrite particles, charge leakage from the ferrite particles is effectively suppressed. If the content of strontium element is 1.0% by mass or less with respect to the total mass of the ferrite particles, the crystal structure of the ferrite particles is regular, and the resistance value and magnetic susceptibility are within appropriate ranges. As a result, fogging is further suppressed, and furthermore, the reproduction of fine lines is improved (for example, suppression of thickening, collapse, or blurring of fine lines).

[0127] From the above viewpoints, the content of strontium element is preferably 0.1% by mass or more and 1.0% by mass or less, more preferably 0.4% by mass or more and 1.0% by mass or less, and still more preferably 0.5% by mass or more and 0.8% by mass or less, relative to the whole ferrite particles.

[0128] The contents of calcium element and strontium element contained in the ferrite particles are measured by fluorescent X-ray analysis. The fluorescent X-ray analysis of the ferrite particles is carried out by the following method.

[0129] Using a fluorescent X-ray analyzer (manufactured by Shimadzu Corporation, XRF1500), qualitative and quantitative analyses are performed under the conditions of X-ray output: 40V / 70mA, measurement area: diameter 10mm, and measurement time: 15 minutes. The elements to be analyzed are selected based on the elements detected by qualitative analysis. Mainly select iron (Fe), manganese (Mn), magnesium (Mg), calcium (Ca), strontium (Sr), oxygen (O), and carbon (C). Referring to the calibration curve data prepared separately, the mass ratio (%) of each element is calculated.

[0130] The volume average particle diameter of the magnetic particles is, for example, 10μm or more and 500μm or less, preferably 20μm or more and 180μm or less, and more preferably 25μm or more and 60μm or less.

[0131] The saturation magnetization of the magnetic particles in a magnetic field of 3000 Oe is, for example, 50 emu / g or more, preferably 60 emu / g or more. The above saturation magnetization is measured using a vibrating sample type magnetometer VSMP10-15 (manufactured by TOEI INDUSTRY CO., LTD.). The measurement sample is placed in a groove with an inner diameter of 7mm and a height of 5mm and set in the device. During the measurement, a magnetic field is applied and scanned up to a maximum of 3000 Oe. Then, the applied magnetic field is reduced, and a hysteresis curve is made on a recording paper. The saturation magnetization, residual magnetization, and coercive force are obtained from the data of the curve.

[0132] The volume resistance (volume resistivity) of the magnetic particles is, for example, 10 5 Ω·cm or more and 10 9 Ω·cm or less, preferably 10 7 Ω·cm or more and 10 9 Ω·cm or less.

[0133] The volume resistance (Ω·cm) of the magnetic particles is measured as follows. The object to be measured is flatly placed on the surface of a circular jig equipped with an electrode plate of 20 cm 2 to form a layer with a thickness of 1mm or more and 3mm or less. On it, the 20 cm 2The layer is clamped by the electrode plates. In order to eliminate the gaps between the objects to be measured, after applying a load of 4 kg to the electrode plates arranged on the layer, the thickness (cm) of the layer is measured. An electrometer and a high-voltage power supply generating device are connected to the upper and lower electrodes of the layer. A high voltage is applied to the two electrodes so that the electric field becomes 103.8 V / cm, and the current value (A) flowing at this time is read. The measurement environment is set to a temperature of 20 °C and a humidity of 50% RH. The calculation formula for the volume resistance (Ω·cm) of the object to be measured is shown in the following formula.

[0134] R = E × 20 / (I - I0) / L

[0135] In the above formula, R represents the volume resistance (Ω·cm) of the object to be measured, E represents the applied voltage (V), I represents the current value (A), I0 represents the current value (A) under the condition of an applied voltage of 0 V, and L represents the thickness (cm) of the layer. The coefficient 20 represents the area (cm 2 ) of the electrode plate.

[0136] <Resin coating layer>

[0137] The carrier for electrostatic image development according to the present embodiment has a resin coating layer on the surface of the magnetic particles.

[0138] As the resin constituting the resin coating layer, styrene-acrylic copolymer; polyolefin resins such as polyethylene and polypropylene; polyvinyl-based or polyvinylidene-based resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymer; linear silicone resin composed of organosiloxane bonds or its modified products; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and chlorotrifluoroethylene; polyester; polyurethane; polycarbonate; amino resins such as urea-formaldehyde resin; epoxy resin, etc. can be cited.

[0139] From the viewpoint of the line density of the obtained image, the resin coating layer preferably contains, for example, an acrylic resin having an aliphatic cyclic structure and an amino group, and more preferably contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group.

[0140] As the aliphatic cyclic structure, for example, cycloalkyl can be preferably selected, and cyclohexyl can be more preferably selected. The acrylic resin having an aliphatic cyclic structure has a small change in charge amount with respect to changes in temperature and humidity, so the line density in the obtained image is stable. In particular, for example, cyclohexyl, which is a stable and large functional group of a 6-membered ring, is preferably used. In addition, the acrylic resin having cyclohexyl is less likely to generate a local charge difference on the surface of the carrier, so unevenness of inorganic particles is less likely to occur and the line density is more stable.

[0141] As an acrylic resin having a cyclohexyl group, specifically, a homopolymer of an acrylic monomer having a cyclohexyl group, a copolymer of an acrylic monomer having a cyclohexyl group and other monomers, etc. can be cited.

[0142] As an acrylic monomer having a cyclohexyl group, for example, cyclohexyl acrylate, cyclohexyl methacrylate, etc. can be cited.

[0143] Moreover, as a structural unit having an aliphatic cyclic structure, a structural unit derived from (meth)acrylic acid cyclohexyl ester can be cited.

[0144] From the viewpoint of the line density of the obtained image, the acrylic resin having a structural unit having an aliphatic cyclic structure preferably contains, for example, 80% by mass or more of the structural unit having an aliphatic cyclic structure.

[0145] Moreover, as an acrylic monomer having an amino group, for example, dialkylaminoalkyl (meth)acrylate can be preferably cited, and dimethylaminoethyl (meth)acrylate can be more preferably cited.

[0146] From the viewpoint of the line density of the obtained image, the acrylic resin having a structural unit having an amino group preferably contains, for example, 0.05% by mass or more and 5% by mass or less of the structural unit having an amino group, and more preferably contains 0.1% by mass or more and 3% by mass or less.

[0147] The acrylic resin having an amino group has, for example, ideal chargeability under high humidity and stable line density. As an acrylic monomer having an amino group, for example, dimethylaminoethyl (meth)acrylate has a small charge difference between low humidity and high humidity, and is therefore particularly preferred.

[0148] When an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group is included, the line density is more likely to be stable. This is because, by using in combination, a relatively large aliphatic cyclic structure part exists around the amino group, whereby the amino group is not easily affected by moisture and can maintain charge, and inorganic fine particles are likely to exist on the surface of the carrier. At the same time, in the aliphatic cyclic structure part, the affinity with the inorganic fine particles with moisture intervening therebetween is suppressed, and therefore excessive attachment of inorganic fine particles to the carrier can be suppressed and the line density is stable. Depending on the size of this structure, for example, a combination of cyclohexyl acrylate and dimethylamino (meth)acrylate is more preferred.

[0149] In the resin coating layer, for the purpose of controlling charging or resistance, inorganic particles other than the aforementioned inorganic particles containing Ti and any one of Ca, Sr, and Ba may be included. Examples of the inorganic particles include: carbon black; metals such as gold, silver, and copper; metal compounds such as barium sulfate, aluminum borate, potassium titanate, titanium oxide, silicon dioxide, zinc oxide, tin oxide, antimony-doped tin oxide, indium tin oxide doped with tin, and zinc oxide doped with aluminum; resin particles coated with a metal, and the like.

[0150] Among them, as the inorganic particles other than the aforementioned inorganic particles containing Ti and any one of Ca, Sr, and Ba, for example, silica particles are preferred.

[0151] With respect to the total mass of the resin coating layer, the content of the inorganic particles other than the aforementioned inorganic particles containing Ti and any one of Ca, Sr, and Ba is, for example, preferably 15% by mass or more and 50% by mass or less, more preferably 20% by mass or more and 40% by mass or less.

[0152] If the resin coating layer is within the above range, the transfer of other toner external additives to the resin coating layer, which may reduce the effect of the aforementioned inorganic particles containing Ti and any one of Ca, Sr, and Ba, is suppressed. And by using silica particles, the transfer of other toner external additives to the resin coating layer is further suppressed.

[0153] As a method for forming a resin coating layer on the surface of magnetic particles, for example, a wet method and a dry method can be cited. The wet method is a method using a solvent that dissolves or disperses the resin constituting the resin coating layer. On the other hand, the dry method is a method that does not use the above solvent.

[0154] As the wet method, for example, an impregnation method in which magnetic particles are impregnated in a resin solution for forming a resin coating layer for coating; a spraying method in which a resin solution for forming a resin coating layer is sprayed onto the surface of magnetic particles; a fluidized bed method in which a resin solution for forming a resin coating layer is sprayed in a state where magnetic particles are flowing in a fluidized bed; a kneading coating method in which magnetic particles and a resin solution for forming a resin coating layer are mixed in a kneading coater and the solvent is removed, and the like.

[0155] The resin solution for forming a resin coating layer used in the wet method is prepared by dissolving or dispersing a resin and other components in a solvent. The solvent is not particularly limited as long as it can dissolve or disperse the resin, and for example, aromatic hydrocarbons such as toluene and xylene; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane can be used.

[0156] As a dry process, for example, a method of heating a mixture of magnetic particles and a resin for forming a resin coating layer in a dry state to form a resin coating layer can be cited. Specifically, for example, magnetic particles and a resin for forming a resin coating layer are mixed in a gas phase and heated and melted to form a resin coating layer.

[0157] The thickness of the resin coating layer is, for example, preferably 0.1 μm or more and 10 μm or less, more preferably 0.3 μm or more and 5 μm or less.

[0158] The exposure ratio of the magnetic particles on the carrier surface is, for example, preferably 2% or more and 20% or less, more preferably 2% or more and 10% or less, and still more preferably 3% or more and 8% or less.

[0159] The exposure ratio of the magnetic particles on the carrier surface is determined by X-ray photoelectron spectroscopy (XPS) using the following method.

[0160] Prepare a carrier as an object and magnetic particles from which the resin coating layer has been removed from the carrier as an object. As a method for removing the resin coating layer from the resin-coated magnetic particles, for example, a method of dissolving the resin component with an organic solvent to remove the resin coating layer, a method of removing the resin coating layer by heating at about 800 °C to disappear the resin component, etc. can be cited. The carrier and the magnetic particles from which the resin coating layer has been removed are used as measurement specimens, and Fe (atomic%) is quantified by XPS, and (Fe of resin-coated magnetic particles) ÷ (Fe of magnetic particles) × 100 is calculated and used as the exposure ratio (%) of the magnetic particles.

[0161] The exposure ratio of the magnetic particles on the carrier surface can be controlled according to the amount of the resin used in the formation of the resin coating layer. The more the amount of the resin relative to the amount of the magnetic particles, the smaller the exposure ratio becomes.

[0162] <Properties of the carrier>

[0163] The volume average particle diameter of the carrier is, for example, preferably 15 μm or more and 510 μm or less, more preferably 20 μm or more and 180 μm or less, and still more preferably 25 μm or more and 60 μm or less.

[0164] From the viewpoint of the line concentration in the obtained image, the fluidity of the carrier for electrostatic image development in the present embodiment is, for example, preferably 26 or more and 34 or less, more preferably 27 or more and 33 or less, and particularly preferably 29 or more and 31 or less. Unless otherwise specified, the unit of fluidity is seconds / 50 g.

[0165] The fluidity of the carrier for electrostatic image development in the present embodiment is set to the value measured in accordance with JIS Z2502 (2020) at 25 °C and 50% RH.

[0166] The saturation magnetization of the carrier in a magnetic field of 1000 Oe is, for example, 40 emu / g or more, preferably 50 emu / g or more. The saturation magnetization is measured in the same manner as that for the magnetic particles, but scanning is performed up to a maximum of 1000 Oe.

[0167] The volume resistivity of the carrier (at 25°C) is, for example, 1×10 7 Ω·cm or more and 1×10 15 Ω·cm or less, preferably 1×10 8 Ω·cm or more and 1×10 14 Ω·cm or less, more preferably 1×10 8 Ω·cm or more and 1×10 13 Ω·cm or less. The volume resistivity of the carrier is measured in the same manner as that for the magnetic particles.

[0168] (Electrostatic image developer)

[0169] The developer according to this embodiment includes a toner and the carrier according to this embodiment.

[0170] The developer according to this embodiment is prepared by mixing the toner and the carrier according to this embodiment in an appropriate mixing ratio. The mixing ratio (mass ratio) of the toner to the carrier is, for example, preferably toner:carrier = 1:100 to 30:100, more preferably 3:100 to 20:100.

[0171] <Electrostatic image developing toner>

[0172] There is no particular limitation on the toner, and known toners can be used. For example, a colored toner containing toner particles containing a binder resin and a colorant can be cited, and an infrared absorbing toner using an infrared absorber instead of the colorant can also be cited. The toner may contain a release agent or various internal additives, external additives, etc.

[0173] -Binder resin-

[0174] As the adhesive resin, for example, vinyl resins composed of homopolymers of monomers such as styrenes (e.g., styrene, p-chlorostyrene, α-methylstyrene, etc.), (meth)acrylates (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), olefins (e.g., ethylene, propylene, butadiene, etc.) or copolymers formed by combining two or more of these monomers can be cited.

[0175] As the adhesive resin, for example, non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, modified rosin, etc., mixtures of them with the vinyl resins, or graft polymers formed by polymerizing vinyl monomers in their coexistence can also be cited.

[0176] These adhesive resins can be used alone or in combination of two or more.

[0177] As the adhesive resin, for example, a polyester resin is preferred. As the polyester resin, for example, well-known polyester resins can be cited.

[0178] The glass transition temperature (Tg) of the polyester resin is, for example, preferably 50°C or higher and 80°C or lower, more preferably 50°C or higher and 65°C or lower.

[0179] The glass transition temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC). More specifically, it is determined from the "extrapolated glass transition start temperature" described in the method for determining the glass transition temperature in JIS K7121-1987 "Method for Measuring the Transition Temperature of Plastics".

[0180] The weight average molecular weight (Mw) of the polyester resin is, for example, preferably 5000 or higher and 1000000 or lower, more preferably 7000 or higher and 500000 or lower. The number average molecular weight (Mn) of the polyester resin is, for example, preferably 2000 or higher and 100000 or lower. The molecular weight distribution Mw / Mn of the polyester resin is, for example, preferably 1.5 or higher and 100 or lower, more preferably 2 or higher and 60 or lower.

[0181] The weight-average molecular weight and the number-average molecular weight are measured by gel permeation chromatography (GPC). In the molecular weight measurement based on GPC, GPC·HLC-8120GPC manufactured by TOSOH CORPORATION is used as the measurement device, and column·TSKgel SuperHM-M (15 cm) manufactured by TOSOH CORPORATION is used in a THF solvent. The weight-average molecular weight and the number-average molecular weight are calculated using a molecular weight calibration curve prepared based on the measurement results and using a monodisperse polystyrene standard sample.

[0182] For example, the combined use of a polyester resin and a vinyl resin as the binder resin is also preferred. The combined use of the two can be a hybrid resin having a chemical bond between a vinyl resin segment and a polyester resin segment (so-called styrene acrylic modified polyester resin), or a mixed resin in which vinyl resin fine particles are mixed in the polyester resin.

[0183] When a polyester resin and a vinyl resin are used in combination, the line concentration in the image is more stable. This is because when the polyester component of the toner particles transferred to the paper during fixing melts to form an image, due to the presence of the vinyl resin that melts slower than the polyester, the thin lines do not become thick and the concentration is stable.

[0184] Examples of the vinyl resin include vinyl-based resins composed of homopolymers of monomers such as styrene-based monomers (e.g., styrene, p-chlorostyrene, α-methylstyrene, etc.), (meth)acrylate-based monomers (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, etc.), ethylenically unsaturated nitrile-based monomers (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ether-based monomers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketone-based monomers (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), olefin-based monomers (e.g., ethylene, propylene, butadiene, etc.) or copolymers formed by combining two or more of these monomers.

[0185] These vinyl resins can be used alone or in combination of two or more.

[0186] As the vinyl resin, from the viewpoint of incompatibility with the polyester resin when melting with the toner, for example, a styrene acrylic resin is preferred.

[0187] The styrene acrylic resin is a copolymer formed by copolymerizing at least a styrene-based monomer (a monomer having a styrene skeleton) and a (meth)acrylic acid-based monomer (a monomer having a (meth)acryloyl group, for example, preferably a monomer having a (meth)acryloyloxy group). The styrene acrylic resin, for example, contains a copolymer of a styrene-based monomer and the aforementioned (meth)acrylate monomer. In addition, the acrylic resin portion in the styrene acrylic resin is a partial structure formed by polymerizing either an acrylic acid-based monomer or a methacrylic acid-based monomer or both. And, "(meth)acrylic acid" is an expression that includes both "acrylic acid" and "methacrylic acid".

[0188] Examples of the styrene-based monomer include styrene, alkyl-substituted styrenes (e.g., α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), halogen-substituted styrenes (e.g., 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), vinylnaphthalene, and the like. The styrene-based monomer can be used alone or in combination of two or more.

[0189] Among these, as the styrene-based monomer, from the viewpoints of easy reactivity, easy controllability of the reaction, and availability, for example, styrene is preferably used.

[0190] As the (meth)acrylic monomer, for example, specifically, (meth)acrylic acid and (meth)acrylic esters can be cited. As the (meth)acrylic ester, for example, (meth)acrylic acid alkyl esters (e.g., n-(meth)acrylate, n-ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-lauryl (meth)acrylate, n-tetradecyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isoamyl (meth)acrylate, pentyl (meth)acrylate, neopentyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, etc.), (meth)acrylic acid aryl esters (e.g., phenyl (meth)acrylate, biphenyl (meth)acrylate, diphenylethyl (meth)acrylate, tert-butylphenyl (meth)acrylate, terphenyl (meth)acrylate, etc.), dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, β-carboxyethyl (meth)acrylate, (meth)acrylamide, etc. can be cited. The (meth)acrylic monomer can be used alone or in combination of two or more. In addition, among these (meth)acrylic esters in the (meth)acrylic monomer, from the viewpoint of improving the fixability of the toner, for example, (meth)acrylic esters having an alkyl group with 2 or more and 14 or less carbon atoms (e.g., preferably 2 or more and 10 or less carbon atoms, more preferably 3 or more and 8 or less carbon atoms) are preferred. Among them, for example, n-butyl (meth)acrylate is preferred, and n-butyl acrylate is particularly preferred.

[0191] The copolymerization ratio (mass basis, styrenic monomer / (meth)acrylic monomer) of the styrenic monomer and the (meth)acrylic monomer is not particularly limited, but is preferably 98 / 2 to 60 / 40.

[0192] From the viewpoint of improving the fixability of the toner, the glass transition temperature (Tg) of the styrene acrylic resin is, for example, preferably 40 °C or higher and 75 °C or lower, more preferably 50 °C or higher and 65 °C or lower.

[0193] Here, the glass transition temperature of the resin is determined from a DSC curve obtained by differential scanning calorimetry (DSC). More specifically, the glass transition temperature of the resin is determined from the "extrapolated glass transition start temperature" described in the method for determining the glass transition temperature in JIS K7121:1987 "Method for Measuring the Transition Temperature of Plastics".

[0194] The weight-average molecular weight and number-average molecular weight of the styrene acrylic resin are measured by gel permeation chromatography (GPC). In the molecular weight measurement based on GPC, GPC·HLC-8120GPC manufactured by TOSOH CORPORATION is used as the measuring device, and column·TSKgel SuperHM-M (15 cm) manufactured by TOSOH CORPORATION is used in a THF solvent. The weight-average molecular weight and number-average molecular weight are calculated using a molecular weight calibration curve prepared based on the measurement results and using a monodisperse polystyrene standard sample.

[0195] The method for producing the styrene acrylic resin is not particularly limited, and various polymerization methods (for example, solution polymerization, precipitation polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc.) can be applied. Also, known operations (for example, batch type, semi-continuous type, continuous type, etc.) can be applied in the polymerization reaction.

[0196] Relative to the entire toner particles, the content of the binder resin is preferably, for example, 40% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and still more preferably 60% by mass or more and 85% by mass or less.

[0197] - Colorant -

[0198] Examples of the colorant include pigments such as carbon black, chrome yellow, Hansa yellow, benzidine yellow, vat yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Vulcan orange, brilliant scarlet, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, phthalocyanine blue, copper oil blue, methylene chloride blue, phthalocyanine green, malachite green oxalate; dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, thiazole-based; and inorganic pigments such as titanium compounds, silicon dioxide, and aluminum.

[0199] The colorant can be used alone or in combination of two or more.

[0200] As needed, surface-treated colorants can be used, and they can be used in combination with dispersants. Moreover, multiple types of colorants can be used in combination.

[0201] Regarding the entire toner particles, the content of the colorant is, for example, preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 15% by mass or less.

[0202] -Release agent-

[0203] As the release agent, for example, hydrocarbon waxes; natural waxes such as carnauba wax, rice bran wax, and candelilla wax; synthetic or mineral / petroleum waxes such as montan wax; ester waxes such as fatty acid esters and montanic acid esters, etc. can be cited. The release agent is not limited to this.

[0204] The melting temperature of the release agent is, for example, preferably 50°C or more and 110°C or less, more preferably 60°C or more and 100°C or less.

[0205] The melting temperature is obtained based on the "melting peak temperature" described in the method for determining the melting temperature of plastics in JIS K7121-1987 from the DSC curve obtained by differential scanning calorimetry (DSC).

[0206] Regarding the entire toner particles, the content of the release agent is, for example, preferably 1% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less.

[0207] -Other additives-

[0208] As other additives, for example, known additives such as magnetic materials, charge control agents, and inorganic powders can be cited. These additives are included in the toner particles as internal additives.

[0209] -Properties of toner particles, etc.-

[0210] The toner particles can be single-layer structured toner particles or so-called core-shell structured toner particles composed of a core (nuclear particles) and a coating layer (shell layer) that coats the core. The core-shell structured toner particles are, for example, composed of a core containing a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer containing a binder resin.

[0211] The volume average particle diameter (D50v) of the toner particles is, for example, preferably 2 μm or more and 10 μm or less, more preferably 4 μm or more and 8 μm or less.

[0212] Regarding the volume average particle diameter (D50v) of the toner particles, it is measured using a Coulter Multisizer II (manufactured by BECKMAN COULTER) with an electrolyte of ISOTON-II (manufactured by BECKMAN COULTER). During the measurement, as a dispersant, in 2 ml of a 5 mass% aqueous solution of a surfactant (for example, sodium alkylbenzenesulfonate is preferred), a measurement sample of 0.5 mg or more and 50 mg or less is added. This is added to 100 ml or more and 150 ml or less of the electrolyte. The electrolyte in which the sample is suspended is dispersed for 1 minute using an ultrasonic disperser, and the particle size distribution of particles in the range of 2 μm or more and 60 μm or less is measured using a Coulter Multisizer II with a pore diameter of 100 μm. The number of sampled particles is 50,000.

[0213] -External Additive-

[0214] As the external additive, for example, inorganic particles can be cited. As such inorganic particles, SiO2, TiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, K2O·(TiO2) n , Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, MgSO4, SrTiO3, BaTiO3, CaTiO3, etc.

[0215] The surface of the inorganic particles as the external additive is preferably subjected to a hydrophobization treatment, for example. The hydrophobization treatment is carried out, for example, by immersing the inorganic particles in a hydrophobization treatment agent. The hydrophobization treatment agent is not particularly limited, and examples thereof include silane-based coupling agents, silicone oils, titanate-based coupling agents, aluminum-based coupling agents, etc. They can be used alone or in combination of two or more.

[0216] The amount of the hydrophobization treatment agent is preferably 1 part by mass or more and 10 parts by mass or less, for example, relative to 100 parts by mass of the inorganic particles.

[0217] As the external additive, resin particles (such as resin particles of polystyrene, polymethyl methacrylate, melamine resin, etc.), cleaning activators (for example, metal salts of higher fatty acids represented by zinc stearate, particles of fluorine-based high molecular weight substances, higher alcohols), etc. can also be cited.

[0218] The addition amount of the external additive is preferably 0.01 mass% or more and 10 mass% or less, more preferably 0.01 mass% or more and 6.0 mass% or less, relative to the toner particles.

[0219] -Method for Manufacturing Toner-

[0220] The toner is obtained by externally adding an external additive to the toner particles after the toner particles are manufactured. The toner particles can be manufactured by any one of a dry process (e.g., kneading and pulverizing method, etc.), a wet process (e.g., aggregation and coalescence method, suspension polymerization method, dissolution and suspension method, etc.). It is not particularly limited to these processes, and known processes can be adopted. Among these, for example, it is preferable to obtain the toner particles by the aggregation and coalescence method.

[0221] <Image Forming Apparatus, Image Forming Method>

[0222] The image forming apparatus and the image forming method according to the present embodiment will be described.

[0223] The image forming apparatus according to the present embodiment includes: an image carrier; a charging member that charges the surface of the image carrier; an electrostatic image forming member that forms an electrostatic image on the surface of the charged image carrier; a developing member that accommodates an electrostatic image developer and develops the electrostatic image formed on the surface of the image carrier into a toner image; a transfer member that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium; and a fixing member that fixes the toner image transferred to the surface of the recording medium. Moreover, as the electrostatic image developer, the electrostatic image developer according to the present embodiment can be applied.

[0224] In the image forming apparatus according to the present embodiment, an image forming method (the image forming method according to the present embodiment) including the following steps is performed: a charging step of charging the surface of the image carrier; an electrostatic image forming step of forming an electrostatic image on the surface of the charged image carrier; a developing step of developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer according to the present embodiment; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; and a fixing step of fixing the toner image transferred to the surface of the recording medium.

[0225] The image forming apparatus according to the present embodiment can be applied to the following well-known image forming apparatuses: an apparatus of a direct transfer method that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an apparatus of an intermediate transfer method that transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer member once, and then transfers the toner image transferred to the surface of the intermediate transfer member to the surface of a recording medium twice; an apparatus including a cleaning member that cleans the surface of the image carrier before charging after transferring the toner image; an apparatus including a static eliminator that irradiates static elimination light to the surface of the image carrier to eliminate static electricity after transferring the toner image and before charging, and the like.

[0226] When the image forming apparatus according to the present embodiment is an apparatus of an intermediate transfer method, the transfer member can be applied to a structure having the following members, for example: an intermediate transfer member to which a toner image is transferred on the surface; a primary transfer member that transfers a toner image formed on the surface of an image carrier to the surface of the intermediate transfer member once; and a secondary transfer member that transfers the toner image transferred to the surface of the intermediate transfer member to the surface of a recording medium twice.

[0227] In the image forming apparatus according to the present embodiment, for example, a portion including a developing member can be a cartridge structure (processing cartridge) detachably attached to the image forming apparatus. As the processing cartridge, a processing cartridge including a developing member that accommodates the electrostatic image developer according to the present embodiment can be preferably used, for example.

[0228] Hereinafter, an example of the image forming apparatus according to the present embodiment is shown, but it is not limited thereto. In the following description, main parts shown in the drawings are described, and other parts are omitted from description.

[0229] Figure 3 It is a schematic configuration diagram showing the image forming apparatus according to the present embodiment.

[0230] Figure 3 The shown image forming apparatus includes electrophotographic first to fourth image forming units 10Y, 10M, 10C, 10K (image forming members) that output images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, 10K are arranged side by side at a predetermined distance from each other in the horizontal direction. These units 10Y, 10M, 10C, 10K can be processing cartridges detachably attached to the image forming apparatus.

[0231] Above each of the units 10Y, 10M, 10C, and 10K, an intermediate transfer belt (an example of an intermediate transfer member) 20 is provided to extend through the units. The intermediate transfer belt 20 is arranged to be wound around a driving roller 22 and a supporting roller 24, and travels in the direction from the first unit 10Y toward the fourth unit 10K. A spring (not shown) or the like applies a force to the supporting roller 24 in a direction away from the driving roller 22, thereby applying tension to the intermediate transfer belt 20 wound around both of them. On the image holding surface side of the intermediate transfer belt 20, an intermediate transfer member cleaning device 30 is provided to face the driving roller 22.

[0232] The yellow, magenta, cyan, and black toner in the toner cartridges 8Y, 8M, 8C, and 8K are respectively supplied to the developing devices (an example of a developing member) 4Y, 4M, 4C, and 4K of the respective units 10Y, 10M, 10C, and 10K.

[0233] The first to fourth units 10Y, 10M, 10C, and 10K have the same structure and operation. Therefore, here, the first unit 10Y that forms a yellow image and is disposed on the upstream side in the traveling direction of the intermediate transfer belt will be described as a representative.

[0234] The first unit 10Y has a photoreceptor 1Y that functions as an image holding member. Around the photoreceptor 1Y, the following components are arranged in sequence: a charging roller (an example of a charging member) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential; an exposure device (an example of an electrostatic image forming member) 3 that exposes the charged surface with a laser beam 3Y based on an image signal after color separation to form an electrostatic image; a developing device (an example of a developing member) 4Y that supplies charged toner to the electrostatic image to develop the electrostatic image; a primary transfer roller 5Y (an example of a primary transfer member) that transfers the developed toner image to the intermediate transfer belt 20; and a photoreceptor cleaning device (an example of a cleaning member) 6Y that removes the toner remaining on the surface of the photoreceptor 1Y after primary transfer.

[0235] The primary transfer roller 5Y is disposed inside the intermediate transfer belt 20 and is arranged at a position facing the photoreceptor 1Y. A bias power source (not shown) for applying a primary transfer bias is connected to each of the primary transfer rollers 5Y, 5M, 5C, and 5K of the respective units. Each bias power source changes the value of the transfer bias applied to each primary transfer roller under the control of a control unit (not shown).

[0236] Hereinafter, the operation of forming a yellow image in the first unit 10Y will be described.

[0237] First, before the operation, the surface of the photoreceptor 1Y is charged to a potential of -600 V to -800 V by the charging roller 2Y.

[0238] The photoreceptor 1Y is formed by laminating a photosensitive layer on a substrate having conductivity (for example, a volume resistivity of 1×10 -6 Ω·cm or less at 20°C). The photosensitive layer is usually of high resistance (the resistance of a general resin), but has the property that the specific resistance of the portion irradiated with the laser beam changes when irradiated with the laser beam. Therefore, according to the yellow image data sent from a control unit (not shown), the laser beam 3Y is irradiated from the exposure device 3 onto the surface of the charged photoreceptor 1Y. Thus, an electrostatic image of the yellow image pattern is formed on the surface of the photoreceptor 1Y.

[0239] The electrostatic image refers to an image formed on the surface of the photoreceptor 1Y by charging, which is a so-called negative latent image. It is formed by the specific resistance of the irradiated portion of the photosensitive layer being reduced by the laser beam 3Y, and the charged charges on the surface of the photoreceptor 1Y flowing, while the charges in the portion not irradiated with the laser beam 3Y remaining.

[0240] As the photoreceptor 1Y advances, the electrostatic image formed on the photoreceptor 1Y rotates to a predetermined development position. Then, at this development position, the electrostatic image on the photoreceptor 1Y is developed by the developing device 4Y and visualized as a toner image.

[0241] In the developing device 4Y, for example, an electrostatic image developer containing at least yellow toner and a carrier is accommodated. The yellow toner is triboelectrically charged by being agitated inside the developing device 4Y, and thus has a charge of the same polarity (negative polarity) as the charge charged on the photoreceptor 1Y and adheres to the developer roller (an example of a developer holding member). Then, the surface of the photoreceptor 1Y passes through the developing device 4Y, so that the yellow toner electrostatically adheres to the latent image portion where the static electricity has been eliminated on the surface of the photoreceptor 1Y, and the latent image is developed by the yellow toner. The photoreceptor 1Y on which the yellow toner image is formed continues to advance at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transferred to a predetermined primary transfer position.

[0242] When the yellow toner image on the photoreceptor 1Y is transferred to the primary transfer position, a primary transfer bias is applied to the primary transfer roller 5Y, and an electrostatic force from the photoreceptor 1Y toward the primary transfer roller 5Y acts on the toner image, thereby transferring the toner image on the photoreceptor 1Y to the intermediate transfer belt 20. The transfer bias applied at this time is of the opposite polarity (+) to the polarity (-) of the toner, and is controlled by a control unit (not shown) in the first unit 10Y to +10 μA, for example.

[0243] On the other hand, the toner remaining on the photoreceptor 1Y is removed and recovered by the photoreceptor cleaning device 6Y.

[0244] The primary transfer bias applied to the primary transfer rollers 5M, 5C, and 5K after the 10M of the second unit is also controlled in accordance with the first unit.

[0245] In this way, the intermediate transfer belt 20 on which the yellow toner image has been transferred in the first unit 10Y is sequentially conveyed through the second to fourth units 10M, 10C, and 10K, so that the toner images of each color are superimposed for multi-transfer.

[0246] The intermediate transfer belt 20 on which the toner images of four colors have been multi-transferred through the first to fourth units reaches the secondary transfer portion constituted by the intermediate transfer belt 20, the support roller 24 in contact with the inner surface of the intermediate transfer belt 20, and the secondary transfer roller (an example of a secondary transfer member) 26 disposed on the image holding surface side of the intermediate transfer belt 20. On the other hand, at a predetermined time, the recording paper (an example of a recording medium) P is supplied to the gap where the secondary transfer roller 26 is in contact with the intermediate transfer belt 20 via the supply mechanism, so that the secondary transfer bias is applied to the support roller 24. The transfer bias applied at this time is a (-) polarity having the same polarity as the polarity (-) of the toner. The electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, so that the toner image on the intermediate transfer belt 20 is transferred to the recording paper P. The secondary transfer bias at this time is determined based on the resistance detected by a resistance detection member (not shown) that detects the resistance of the secondary transfer portion and is voltage-controlled.

[0247] Then, the recording paper P is fed into the crimping portion (crimping portion) of a pair of fixing rollers in the fixing device (an example of a fixing member), and the toner image is fixed on the recording paper P to form a fixed image.

[0248] As the recording paper P for transferring the toner image, for example, ordinary paper used in electrophotographic copiers, printers, etc. can be cited. As the recording medium, in addition to the recording paper P, OHP sheets, etc. can also be cited.

[0249] In order to further improve the smoothness of the surface of the fixed image, for example, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper obtained by coating the surface of ordinary paper with resin or the like, art paper for printing, etc. can be preferably used.

[0250] The recording paper P on which the color image has been fixed is conveyed toward the discharge portion, thus ending a series of color image forming operations.

[0251] <Processing Cartridge>

[0252] The processing cartridge according to the present embodiment will be described.

[0253] The processing cartridge according to the present embodiment is a processing cartridge that includes a developing member and is detachably attached to an image forming apparatus. The developing member accommodates the electrostatic image developer according to the present embodiment and develops an electrostatic image formed on the surface of an image carrier into a toner image using the electrostatic image developer.

[0254] The processing cartridge according to the present embodiment is not limited to the above structure, and may also have a structure that includes a developing member and, as needed, at least one other member selected from other members such as an image carrier, a charging member, an electrostatic image forming member, and a transfer member.

[0255] Hereinafter, an example of the processing cartridge according to the present embodiment is shown, but it is not limited thereto. In the following description, the main parts shown in the drawings are described, and other parts are omitted.

[0256] Figure 4 It is a schematic structural diagram showing the processing cartridge according to the present embodiment.

[0257] Figure 4 The shown processing cartridge 200 is configured, for example, by integrally combining and holding a photosensitive drum 107 (an example of an image carrier), a charging roller 108 (an example of a charging member) around the photosensitive drum 107, a developing device 111 (an example of a developing member), and a photosensitive drum cleaning device 113 (an example of a cleaning member) using a housing 117 having a mounting rail 116 and an opening 118 for exposure, and is made into a cartridge.

[0258] Figure 4 In this, 109 represents an exposure device (an example of an electrostatic image forming member), 112 represents a transfer device (an example of a transfer member), 115 represents a fixing device (an example of a fixing member), and 300 represents a recording paper (an example of a recording medium).

[0259] Examples

[0260] Hereinafter, the present embodiment will be described in detail by way of examples, but the present embodiment is not limited by any of these examples. In the following description, "parts" and "%" are based on mass unless otherwise specified.

[0261] <Measurement of BET specific surface area of magnetic particles>

[0262] Using an arbitrary filter, the toner was removed from the electrostatic image developer by blowing air. Then, the coating film was removed with a solvent to obtain magnetic particles.

[0263] The obtained magnetic particles were placed in a cell of a SA3100 specific surface area measuring device (manufactured by BECKMAN COULTER), degassed at 60 °C for 120 minutes, purged with a mixed gas of nitrogen and helium (volume ratio 30:70), and measured by the continuous one-point method.

[0264] <Measurement of roundness distribution and average roundness of inorganic particles>

[0265] Regarding the average roundness of inorganic particles, the roundness was determined by image analysis of at least 300 inorganic particles, a roundness distribution was created, and the average roundness was obtained by taking the average of the roundness. Also, the roundness corresponding to 84% cumulative was determined from the roundness distribution. The inorganic particles are particles present on the surface of a carrier after removing toner from an electrostatic image developer using an arbitrary filter and blowing air. The inorganic particles were identified and measured based on the elements of each particle on the carrier by energy dispersive X-ray analysis (SEM-EDX).

[0266] <Measurement of the ratio Mx / Mt of the molar amount Mt of Ti to the total molar amount Mx of Ca, Sr, and Ba>

[0267] The elements on the carrier were mapped by energy dispersive X-ray analysis (SEM-EDX). The titanate compound was identified based on the elements of each particle on the carrier, and the coating rate was calculated.

[0268] Furthermore, the net intensity was measured by SEM-EDX, and the net intensity ratio of particles in which Ti and Ca / Sr / Ba were synchronized was calculated.

[0269] A calibration curve was prepared separately, molar conversion was performed, the molar amounts (Mt and Mx) were determined, and Mx / Mt was calculated.

[0270] <Volume average particle size of the carrier>

[0271] An arbitrary filter was used and air was blown to remove toner from the electrostatic image developer, and the carrier was taken out. The particle size distribution of the carrier was measured using a laser diffraction / scattering particle size distribution measuring device (LS Particle Size Analyzer: LS13 320, manufactured by BECKMAN COULTER). For the particle size range (interval) obtained by dividing the obtained particle size distribution, the volume cumulative distribution was plotted from the small particle size side, and the particle size corresponding to 50% cumulative was defined as the volume average particle size D50.

[0272] <Preparation of toner>

[0273] [Preparation of resin particle dispersion (1)]

[0274] · Ethylene glycol (manufactured by FUJIFILM Wako Pure Chemical Corporation): 37 parts

[0275] · Neopentyl glycol (manufactured by FUJIFILM Wako Pure Chemical Corporation): 65 parts

[0276] · 1,9-Nonanediol (manufactured by FUJIFILM Wako Pure Chemical Corporation): 32 parts

[0277] · Terephthalic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation): 96 parts

[0278] The above materials were charged into a flask, and the temperature was raised to 200 °C over 1 hour. After confirming that they were uniformly stirred in the reaction system, 1.2 parts of dibutyltin oxide were added. While distilling off the generated water, the temperature was raised to 240 °C over 6 hours, and stirring was continued at 240 °C for 4 hours to obtain a polyester resin (acid value 9.4 mgKOH / g, weight-average molecular weight 13,000, glass transition temperature 62 °C). The polyester resin was directly transferred to an emulsifying disperser (Cavitron CD1010, manufactured by EUROTEC) at a rate of 100 g per minute in a molten state. In addition, a 0.37% concentration of dilute ammonia water prepared by diluting reagent ammonia water with deionized water was placed in a tank and transferred to the emulsifying disperser at a rate of 0.1 liter per minute simultaneously with the polyester resin while being heated to 120 °C with a heat exchanger. The emulsifying disperser was operated under the conditions of a rotor speed of 60 Hz and a pressure of 5 kg / cm 2 to obtain a resin particle dispersion (1) having a volume-average particle diameter of 160 nm and a solid content of 30%.

[0279] 〔Preparation of resin particle dispersion (2)〕

[0280] · Sebacic acid (manufactured by Tokyo Chemical Industry Co., Ltd.): 81 parts

[0281] · Hexanediol (FUJIFILM Wako Pure Chemical Corporation): 47 parts

[0282] The above materials were charged into a flask, and the temperature was raised to 160 °C over 1 hour. After confirming that the materials were uniformly stirred in the reaction system, 0.03 parts of dibutyltin oxide were added. While distilling off the generated water, the temperature was raised to 200 °C over 6 hours, and stirring was continued at 200 °C for 4 hours. Then, the reaction solution was cooled, and solid-liquid separation was performed. The solid substance was dried at 40 °C under reduced pressure to obtain a polyester resin (C1) (melting point 64 °C, weight-average molecular weight 15,000).

[0283] · Polyester resin (C1): 50 parts

[0284] · Anionic surfactant (NEOGEN SC, manufactured by DKS Co., Ltd.): 2 parts

[0285] · Deionized water: 200 parts

[0286] The above materials were heated to 120 °C and sufficiently dispersed using a homogenizer (ULTRA TURRAX T50, manufactured by IKA), and then dispersed using a pressure jet homogenizer. Recovery was carried out when the volume average particle diameter reached 180 nm to obtain a resin particle dispersion (2) with a solid content of 20%.

[0287] 〔Preparation of colorant particle dispersion (1)〕

[0288] · Blue-green pigment [Pigment Blue 15:3, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.]: 10 parts

[0289] · Anionic surfactant (NEOGEN SC, manufactured by DKS Co., Ltd.): 2 parts

[0290] · Ion-exchanged water: 80 parts

[0291] The above materials were mixed and dispersed using a high-pressure impact disperser (ULTIMAIZER HJP30006, manufactured by SUGINOMACHINE LIMITED) for 1 hour to obtain a colorant particle dispersion (1) with a volume average particle diameter of 180 nm and a solid content of 20%.

[0292] 〔Preparation of mold release agent particle dispersion (1)〕

[0293] · Paraffin (HNP-9, manufactured by NIPPON SEIRO CO., LTD.): 50 parts

[0294] · Anionic surfactant (NEOGEN SC, manufactured by DKS Co., Ltd.): 2 parts

[0295] · Deionized water: 200 parts

[0296] The above materials were heated to 120 °C and thoroughly dispersed using a homogenizer (ULTRA TURRAX T50, IKA), and then dispersed using a pressure jet homogenizer. Recovery was performed when the volume average particle size reached 200 nm, obtaining a mold release agent particle dispersion (1) with a solid content of 20%.

[0297] 〔Preparation of toner (1)〕

[0298] · Resin particle dispersion (1): 150 parts

[0299] · Resin particle dispersion (2): 50 parts

[0300] · Colorant particle dispersion (1): 25 parts

[0301] · Mold release agent particle dispersion (1): 35 parts

[0302] · Polyaluminum chloride: 0.4 part

[0303] · Ion-exchanged water: 100 parts

[0304] The above materials were put into a round stainless steel flask and thoroughly mixed and dispersed using a homogenizer (ULTRA TURRAX T50, IKA). While stirring the contents of the flask, it was heated to 48 °C using an oil bath for heating. After maintaining the reaction system at 48 °C for 60 minutes, 70 parts of resin particle dispersion (1) were slowly added. Then, the pH was adjusted to 8.0 using a 0.5 mol / L aqueous sodium hydroxide solution, the flask was sealed, and the seal of the stirring shaft was set as a magnetic seal. While continuing to stir, it was heated to 90 °C and maintained for 30 minutes. Then, it was cooled at a rate of 5 °C / minute, and solid-liquid separation was performed, and it was thoroughly washed with deionized water. Then, solid-liquid separation was performed again, and it was redispersed in ion-exchanged water at 30 °C, stirred at a rotation speed of 300 rpm (revolutions per minute) for 15 minutes and washed. This washing operation was further repeated 6 times, and solid-liquid separation was performed when the pH of the filtrate reached 7.54 and the conductivity reached 6.5 μS / cm, and vacuum drying was continued for 24 hours, obtaining toner particles with a volume average particle size of 5.7 μm.

[0305] 100 parts of the above toner particles were mixed with 2.5 parts of silica particles (surface hydrophobized with hexamethyldisilazane, average primary particle size 40 nm) using a Henschel mixer, obtaining toner (1).

[0306] 〔Preparation of resin particle dispersion (3)〕

[0307] · 1,10 - Decanedicarboxylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation): 260 parts

[0308] · 1,6 - Hexanediol (manufactured by FUJIFILM Wako Pure Chemical Corporation): 167 parts

[0309] · Dibutyltin oxide (catalyst): 0.3 part

[0310] The above materials were charged into a flask, the air in the flask was replaced with nitrogen to create an inert environment, and stirring reflux was carried out for 5 hours at 180 °C by mechanical stirring. Then, the temperature was gradually raised to 230 °C under reduced pressure and stirred for 2 hours. When it became viscous, air cooling was carried out to stop the reaction. Thus, a crystalline polyester with a weight - average molecular weight of 12,500 and a melting temperature of 73 °C was obtained. 90 parts of the crystalline polyester resin, 1.8 parts of an anionic surfactant (TaycaPower, manufactured by TAYCA Co., Ltd., solid content 12%, sodium dodecylbenzenesulfonate), and 210 parts of ion - exchanged water were mixed, heated to 120 °C, dispersed using a homogenizer (ULTRA TURRAX T50 manufactured by IKA), and then subjected to a dispersion treatment for 1 hour using a pressure - jet type high - shear homogenizer to obtain a resin particle dispersion (3) with a volume - average particle diameter of 195 nm and a solid content of 30%.

[0311] 〔Synthesis of amorphous polyester resin (A)〕

[0312] · Terephthalic acid: 68 parts

[0313] · Fumaric acid: 32 parts

[0314] · Ethylene glycol: 42 parts

[0315] · 1,5 - Pentanediol: 47 parts

[0316] The above materials were placed in a flask equipped with a stirring device, a nitrogen inlet tube, a temperature sensor, and a distillation column. The temperature was raised to 220 °C over 1 hour under a nitrogen stream, and 1 part of tetraethoxytitanium was added per 100 parts in total of the above materials. While distilling off the generated water, the temperature was raised to 240 °C over 0.5 hour and the dehydration condensation reaction was continued at 240 °C for 1 hour, and then the reaction product was cooled. Thus, an amorphous polyester resin (A) with a weight - average molecular weight of 97000 and a glass transition temperature of 60 °C was obtained.

[0317] [Preparation of Amorphous Polyester Resin Particle Dispersion (A1)]

[0318] After putting 40 parts of ethyl acetate and 25 parts of 2-butanol in a container equipped with a temperature control member and a nitrogen replacement member to prepare a mixed solvent, 100 parts of amorphous polyester resin (A) was gradually added and dissolved therein. Then, 10% aqueous ammonia solution (in an amount equivalent to 3 times the acid value of the resin in molar ratio) was added thereto and stirred for 30 minutes. Next, the inside of the container was replaced with dry nitrogen, and the temperature was maintained at 40 °C. While stirring the mixed solution, 400 parts of ion-exchanged water was added dropwise and emulsified. After the addition was completed, the emulsion was restored to 25 °C, and a resin particle dispersion in which resin particles with a volume average particle diameter of 195 nm were dispersed was obtained. Ion-exchanged water was added to this resin particle dispersion, and the solid content was adjusted to 20% to obtain an amorphous polyester resin particle dispersion (4).

[0319] [Preparation of Styrene Acrylic Resin Particle Dispersion (S1)]

[0320] · Styrene: 375 parts

[0321] · n-Butyl Acrylate: 25 parts

[0322] · Acrylic Acid: 2 parts

[0323] · Dodecanethiol: 24 parts

[0324] · Carbon Tetrabromide: 4 parts

[0325] In a flask, a mixture obtained by mixing and dissolving the above materials was dispersed and emulsified in a surfactant solution prepared by dissolving 6 parts of a nonionic surfactant (manufactured by Sanyo Chemical Industries, Ltd., NONIPOL 400) and 10 parts of an anionic surfactant (manufactured by Tayca Power, TAYCA Co., Ltd., solid content 12%, sodium dodecylbenzenesulfonate) in 550 parts of ion-exchanged water. Then, while stirring the inside of the flask, an aqueous solution prepared by dissolving 4 parts of ammonium persulfate in 50 parts of deionized water was added dropwise over 20 minutes. Next, after nitrogen replacement, while stirring the inside of the flask, it was heated in an oil bath until the content reached 70 °C, and the emulsion polymerization was continued while maintaining at 70 °C for 5 hours. Thus, a resin particle dispersion in which resin particles with a volume average particle diameter of 150 nm were dispersed was obtained. Ion-exchanged water was added to this resin particle dispersion, and the solid content was adjusted to 20% to obtain a styrene acrylic resin particle dispersion (S1).

[0326] <Preparation of Color Toner>

[0327] 〔Production of Cyan-Green Toner (CT1)〕

[0328] - First Agglomerate Particle Formation Step -

[0329] · Deionized water: 200 parts

[0330] · Colorant particle dispersion (Cy1): 15 parts

[0331] · Release agent particle dispersion (W1): 10 parts

[0332] · Styrene-acrylic resin particle dispersion (S1): 60 parts

[0333] · Amorphous polyester resin particle dispersion (B1): 10 parts

[0334] · Amorphous polyester resin particle dispersion (A1): 310 parts

[0335] The above materials were put into a round stainless steel flask, nitric acid of 0.1 N (= 0.1 mol / L) was added, and after adjusting the pH to 3.5, an aqueous magnesium chloride solution prepared by dissolving 6 parts of magnesium chloride in 30 parts of ion-exchanged water was added. After dispersing at 30 °C using a homogenizer (ULTRA-TURRAX T50 manufactured by IKA), it was heated to 45 °C in a heating oil bath and maintained until the volume average particle diameter became 4.5 μm.

[0336] - Second Agglomerate Particle Formation Step -

[0337] Next, 5 parts of the styrene-acrylic resin fine particle dispersion (S1) was added dropwise and maintained for 30 minutes. A total of 4 times of addition of 5 parts of the styrene-acrylic resin fine particle dispersion (S1) was carried out every 30 minutes. Then, while continuing stirring, the pH was adjusted to 9.0 using a 1 N (= 0.1 mol / L) aqueous sodium hydroxide solution.

[0338] - Fusion / Unification Step -

[0339] Next, while continuing stirring, the temperature was raised to 85 °C at a rate of 0.5 °C / minute, maintained at 85 °C for 3 hours, and then cooled to 30 °C at a rate of 15 °C / minute (first cooling). Then, it was heated (re-heated) to 85 °C at a rate of 0.2 °C / minute, maintained for 30 minutes, and then cooled (second cooling) to 30 °C at a rate of 0.5 °C / minute. Then, the solid component was filtered out, washed with ion-exchanged water and dried to obtain cyan-green toner particles with a volume average particle diameter of 4.7 μm.

[0340] 100 parts of the above toner particles and 3 parts of silica particles (surface-hydrophobized with hexamethyldisilazane, average primary particle size of 40 nm) were mixed using a Henschel mixer to obtain toner (2).

[0341] <Fabrication of Magnetic Particles>

[0342] [Fabrication of Magnetic Particle 1]

[0343] 1,307 parts of Fe2O3, 712 parts of Mn(OH)2, 10.5 parts of Mg(OH)2, and 20 parts of CaCO3 were mixed, and polycarboxylate, water, and zirconia beads with a diameter of 1 mm were added as dispersants, followed by disintegration and mixing using a sand mill. The zirconia beads were filtered out, and after drying the filtrate, precalcination was carried out using a rotary kiln under the conditions of a rotation speed of 20 rpm, a temperature of 900 °C, and a time of 2 hours. Polycarboxylate and water were added as dispersants to the obtained precalcined product, 8 parts of polyvinyl alcohol were further added, and pulverization and mixing were carried out using a wet ball mill for 5 hours. The volume average particle size of the obtained pulverized product was 1.2 μm. Subsequently, granulation was carried out using a spray dryer to a particle size of 34 μm. The obtained granulated product was calcined formally using an electric furnace under an oxygen-nitrogen mixed environment with an oxygen concentration of 1 vol% at a temperature of 1,420 °C for 6 hours. Furthermore, the obtained calcined product was disintegrated and classified. After the disintegration and classification of the obtained particles, heating was carried out using a rotary kiln at 15 rpm and 900 °C for 2 hours (post-process), and then classification was carried out to obtain magnetic particle 1. The volume average particle size of magnetic particle 1 was 32 μm, and the BET specific surface area was 0.18 m 2 / g.

[0344] [Fabrication of Magnetic Particles 2 - 10]

[0345] As recorded in Table 1, the raw materials and various conditions were changed, and except for this, magnetic particles 2 - 10 were fabricated in the same manner as the fabrication of magnetic particle 1, respectively.

[0346]

[0347] <Fabrication of Inorganic Particles>

[0348] [Fabrication of Inorganic Particle 1]

[0349] Collect 0.7 moles of metatitanic acid as a desulfurized and peptized titanium source in terms of TiO₂, and place it in a reaction vessel. Next, 0.77 moles of an aqueous strontium chloride solution was added to the reaction vessel so that the SrO / TiO₂ molar ratio became 1.1. Next, a solution prepared by dissolving silicon dioxide in nitric acid in an amount such that the amount of silicon was 2.5 moles per 100 moles of strontium was added to the reaction vessel. The initial TiO₂ concentration in the mixed solution of the three materials was made 0.75 mol / L. Next, the mixed solution was stirred, and the mixed solution was heated to 90 °C. While maintaining the liquid temperature at 90 °C and stirring, 153 mL of 10N (= 10 mol / L) aqueous sodium hydroxide solution was added over 4 hours. Furthermore, stirring was continued for 1 hour while maintaining the liquid temperature at 90 °C. Next, the reaction solution was cooled to 40 °C, hydrochloric acid was added until the pH became 5.5, and stirring was carried out for 1 hour. Next, the precipitate was washed by repeating decantation and redispersion in water. Hydrochloric acid was added to the slurry containing the washed precipitate to adjust the pH to 6.5, and the solid component was filtered out and dried. An ethanol solution of i-butyltrimethoxysilane (i-BTMS) in an amount such that i-BTMS was 20 parts per 100 parts of the solid component was added to the dried solid component, and stirring was carried out for 1 hour. The solid component was filtered out, and the solid component was dried in the atmosphere at 130 °C for 7 hours to obtain inorganic particles 1.

[0350] The roundness can be adjusted according to the temperature of the mixed solution and the amount of sodium hydroxide added. By setting the temperature of the mixed solution higher, the value of the roundness can be increased, and by lowering the temperature of the mixed solution, the value of the roundness can be decreased. Also, the roundness can be adjusted according to the amount of sodium hydroxide added. If the amount of sodium hydroxide is small, the value of the roundness becomes large, and if the amount of sodium hydroxide is large, the value of the roundness becomes small. The roundness is adjusted according to the temperature of the mixed solution and the amount of sodium hydroxide.

[0351] The roundness at 84% cumulative can be adjusted according to the addition time of sodium hydroxide. If the addition time is long, the value of the roundness at 84% cumulative becomes large, and if the addition time is short, the value of the roundness at 84% cumulative becomes small.

[0352] 〔Production of Inorganic Particles 2 to 17〕

[0353] As described in Table 2, the type of dopant, the time taken for the dropwise addition of 10N aqueous sodium hydroxide solution were adjusted to adjust the average particle size, the average roundness, and the roundness at 84% cumulative. Other than that, inorganic particles 2 to 17 were produced in the same manner as the production of inorganic particles 1. In addition, regarding inorganic particles 7, an amount such that the amount of silicon was 12.5 moles per 100 moles of strontium was added, and other than that, it was produced in the same manner as the production of inorganic particles 1. In the dopant column of inorganic particles 7 in Table 2, it is described as "Si rich".

[0354] [Table 2]

[0355]

[0356] In Table 2 and Table 4 described later, Mx / Mt represents the ratio of the molar amount Mt of Ti in the inorganic particles to the total molar amount Mx of Ca, Sr, and Ba.

[0357] <Preparation of Coating Agent 1>

[0358] · Cyclohexyl methacrylate-dimethylaminoethyl methacrylate copolymer (polymerization mass ratio 99.5:0.5, weight-average molecular weight 80,000): 36 parts

[0359] · Carbon black (VXC72, Cabot): 4 parts

[0360] · Melamine resin particles (EPOSTAR S, manufactured by NIPPON SHOKUBAI CO., LTD.): 3 parts

[0361] · Toluene: 180 parts

[0362] · Isopropyl alcohol: 30 parts

[0363] The above materials and glass beads (diameter 1 mm, the same amount as toluene) were put into a sand mill (Kansai Paint Co., Ltd.) and stirred at a rotation speed of 1,200 rpm for 30 minutes to prepare Coating Agent 1.

[0364] <Preparation of Coating Agent 2>

[0365] · Homopolymer of cyclohexyl methacrylate (weight-average molecular weight 80,000): 36 parts

[0366] · Carbon black (VXC72, Cabot): 4 parts

[0367] · Melamine resin particles (EPOSTAR S, manufactured by NIPPON SHOKUBAI CO., LTD.): 3 parts

[0368] · Toluene: 180 parts

[0369] · Isopropyl alcohol: 30 parts

[0370] The above materials and glass beads (diameter 1 mm, the same amount as toluene) were put into a sand mill (Kansai Paint Co., Ltd.) and stirred at a rotation speed of 1,200 rpm for 30 minutes to prepare Coating Agent 2.

[0371] <Preparation of Coating Agent 3>

[0372] · Cyclohexyl methacrylate-dimethylaminoethyl methacrylate copolymer (polymerization mass ratio 99.5:0.5, weight-average molecular weight 80,000): 36 parts

[0373] · Carbon black (VXC72, Cabot): 4 parts

[0374] · Melamine resin particles (EPOSTAR S, manufactured by NIPPON SHOKUBAI CO., LTD.): 3 parts

[0375] · Inorganic particles 1: 15 parts

[0376] · Toluene: 180 parts

[0377] · Isopropyl alcohol: 30 parts

[0378] The above materials and glass beads (diameter 1 mm, the same amount as toluene) were put into a sand mill (Kansai Paint Co., Ltd.), and stirred at a rotation speed of 1,200 rpm for 30 minutes to prepare Coating Agent 3.

[0379] <Preparation of Coating Agent 4>

[0380] The cyclohexyl methacrylate-dimethylaminoethyl methacrylate copolymer in Coating Agent 1 was changed to a methyl methacrylate polymer (weight-average molecular weight 50,000), and Coating Agent 4 was prepared in the same manner as the preparation of Coating Agent 1 except for this.

[0381] (Examples 1 to 27 and Comparative Examples 1 to 5)

[0382] <Production of Carrier for Electrostatic Image Development>

[0383] The inorganic particles described in Table 3 in the amount described in Table 3 were put into a vacuum degassing kneader, and further the coating agent described in Table 3 in the amount described in Table 3 was put in. While stirring, the temperature was raised and the pressure was reduced. The pressure was reduced to atmospheric pressure - 200 mmHg at 60 °C and stirred for 15 minutes, and then the temperature was raised and the pressure was reduced to 94 °C / atmospheric pressure - 720 mmHg and stirred for 30 minutes. Then, the reduced pressure was released and stirred and dried for 10 minutes. The obtained particles were sieved with a sieve having a pore size of 75 μm to obtain Carriers 1 to 14 respectively.

[0384] [Table 3]

[0385]

[0386] 1,500 portions of the carrier described in Table 4 below were put into a V-type mixer. Next, 0.75 portions of the inorganic particles described in Table 4 were put into the V-type mixer and stirred for 30 minutes under the condition of 25 rpm (revolutions per minute), and carriers for electrostatic image development were obtained respectively.

[0387] <Production of Electrostatic Image Developer>

[0388] Regarding the carriers for electrostatic image development obtained in the V-type mixer, 120 portions of toner (1) were put into the V-type mixer and stirred for 20 minutes under the condition of 25 rpm. Then, sieving was carried out with a sieve having a pore size of 75 μm, and developers 1 to 30 (electrostatic image developers) were obtained respectively.

[0389] <Evaluation of Line Concentration and White Spot Inhibiting Property>

[0390] The electrostatic image developer as the object was loaded at the cyan position of ApeosPrint C5570 (manufactured by FUJIFILM Business Innovation Corp.). Five lines with a length of 20 cm and 1.0 pt were printed on A4 paper at intervals of 2 cm. Printing of 3,000 sheets was carried out at a printing speed of 55 sheets per minute. The line concentrations of the first printed sheet and the 3,000th printed sheet were compared. At this time, the parameters of C5570 were adjusted so that the toner concentration of the electrostatic image developer was fixed at 6%, and printing was carried out under the conditions of 12°C and 10% RH. Next, print Figure 1 the image IM shown, and in Figure 1 the image IM shown, the printing concentration of the part R shown in Figure 2 was confirmed. In addition, the image concentration of the high-concentration image HD was set to 1.8, and the image concentration of the low-concentration image LD was set to 0.5 (in addition, each image concentration is a cyan concentration measurement value based on the X-Rite404 concentration measuring instrument manufactured by X-Rite company).

[0391] -Comparison of Line Concentrations between the First Sheet L1 and the 3,000th Sheet L3-

[0392] G5: Even when magnified 20 times, no difference in image concentration between L1 and L3 was observed

[0393] G4: There was no difference when visually observed, but when magnified 20 times, it was confirmed that the line of L3 was slightly thinner

[0394] G3: There was no difference when visually observed, but L3 was lighter when magnified 20 times

[0395] G2: It was visually confirmed that L3 was lighter

[0396] G1: The line of L3 is light and thin.

[0397] - Evaluation of white spot suppression ( Figure 1 Image comparison)-

[0398] G5: Figure 2 The part shown has no abnormality.

[0399] G4: Figure 2 The part shown is slightly light.

[0400] G3: Figure 2 The part shown is significantly light.

[0401] G2: Figure 2 The part shown has white spots.

[0402] G1: Figure 2 The part shown is largely missing.

[0403] The evaluation results are shown together in Table 4.

[0404]

[0405] The titanium dioxide particles described in Table 4 are T805 manufactured by NIPPON AEROSIL CO., LTD.

[0406] As shown in Table 4, the electrostatic image developing carriers of Examples 1 to 27 are superior in line density and white spot suppression in the obtained images compared with the electrostatic image developing carriers of Comparative Examples 1 to 5.

[0407] (Example 28)

[0408] In the toner (1), the amount of silica particles mixed with a Henschel mixer was set to 3.4 parts by mass, and after mixing, 1.5 parts by weight of inorganic particles 1 were added and mixed with a Henschel mixer. Other than this, the toner (2) was produced in the same manner as the production of the toner (1).

[0409] Next, the carrier 1 and the toner 2 were mixed with a V-type mixer under the same conditions as the production of the developer 1 to obtain the developer 32.

[0410] As a result of conducting the above evaluations, the line density evaluation of the developer 32 was G4, and the white spot suppression evaluation was G4.

[0411] (1) A carrier for electrostatic image development, which has magnetic particles and a resin coating layer on the surface of the magnetic particles, has inorganic particles on the surface or contains inorganic particles in the resin coating layer, the inorganic particles contain Ti and any one of Ca, Sr, and Ba, the average roundness of the primary particles of the inorganic particles is 0.82 or more and 0.94 or less, and the BET specific surface area of the magnetic particles is 0.12 m 2 / g or more and 0.24 m 2 / g or less.

[0412] (2) The carrier for electrostatic image development according to (1), wherein

[0413] the roundness of the inorganic particles at 84% cumulative is more than 0.92.

[0414] (3) The carrier for electrostatic image development according to (1) or (2), wherein

[0415] the ratio Mx / Mt of the molar amount Mt of Ti in the inorganic particles to the total molar amount Mx of Ca, Sr, and Ba is 0.65 or more and 0.90 or less.

[0416] (4) The carrier for electrostatic image development according to any one of (1) to (3), wherein

[0417] the fluidity of the carrier for electrostatic image development is 26 or more and 34 or less.

[0418] (5) The carrier for electrostatic image development according to any one of (1) to (4), wherein

[0419] the resin coating layer contains an acrylic resin having an aliphatic cyclic structure and an amino group.

[0420] (6) The carrier for electrostatic image development according to (5), wherein

[0421] the resin coating layer contains an acrylic resin having a structural unit with an aliphatic cyclic structure and a structural unit with an amino group.

[0422] (7) The carrier for electrostatic image development according to any one of (1) to (6), wherein

[0423] the average particle size of the carrier for electrostatic image development is 30 μm or more and 38 μm or less.

[0424] (8) An electrostatic image developer, which contains the carrier for electrostatic image development according to any one of (1) to (7) and a toner.

[0425] (9) A processing cartridge includes a developing member that accommodates the electrostatic image developer as described in (8) and develops an electrostatic image formed on the surface of an image carrier into a toner image using the electrostatic image developer, and the processing cartridge is detachably mounted on an image forming apparatus.

[0426] (10) An image forming method includes: a charging step of charging at least an image carrier; an exposure step of forming an electrostatic latent image on the surface of the image carrier; a developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic image developer to form a toner image; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a transfer body; and a fixing step of fixing the toner image, and the electrostatic image developer is the electrostatic image developer as described in (8).

[0427] (11) An image forming apparatus includes: an image carrier; a charging member that charges the image carrier; an exposure member that exposes the charged image carrier to form an electrostatic latent image on the image carrier; a developing member that develops the electrostatic latent image with an electrostatic image developer to form a toner image; a transfer member that transfers the toner image from the image carrier to a transfer body; and a fixing member that fixes the toner image, and the electrostatic image developer is the electrostatic image developer as described in (8).

[0428] According to the invention according to (1), there is provided a carrier for electrostatic image development as follows. Compared with the case where the inorganic particles are titanium dioxide, or the average roundness of the primary particles of the inorganic particles is less than 0.82 or more than 0.94, or the BET specific surface area of the magnetic particles is less than 0.12 m 2 / g or more than 0.24 m 2 / g, the line density and white spot suppression in the obtained image are excellent.

[0429] According to the invention according to (2), there is provided a carrier for electrostatic image development as follows. Compared with the case where the roundness of the inorganic particles at 84% cumulative is 0.92 or less, the line density and white spot suppression in the obtained image are more excellent.

[0430] According to the invention according to (3), there is provided a carrier for electrostatic image development as follows. Compared with the case where the ratio Mx / Mt of the total molar amount Mx of Ca, Sr, and Ba to the molar amount Mt of Ti in the inorganic particles is less than 0.65 or more than 0.90, the line density and white spot suppression in the obtained image are more excellent.

[0431] According to the invention related to (4), there is provided a carrier for electrostatic image development as follows. Compared with the case where the fluidity is less than 26 or more than 34, the line density in the obtained image is more excellent.

[0432] According to the invention related to (5) or (6), there is provided a carrier for electrostatic image development as follows. Compared with the case where the resin coating layer contains only an acrylic resin having an aliphatic cyclic structure and no amino group, the line density in the obtained image is more excellent.

[0433] According to the invention related to (7), there is provided a carrier for electrostatic image development as follows. Compared with the case where the average particle diameter is less than 30 μm or more than 38 μm, the line density in the obtained image is more excellent.

[0434] According to the inventions related to (8) to (11), there are provided an electrostatic image developer, a processing cartridge, an image forming method, or an image forming apparatus as follows. Compared with the case where the inorganic particles in the carrier for electrostatic image development are titanium dioxide, or the average roundness of the primary particles of the inorganic particles is less than 0.82 or more than 0.94, or the BET specific surface area of the magnetic particles is less than 0.12 m 2 / g or more than 0.24 m 2 / g, the line density and white spot suppression property in the obtained image are excellent.

[0435] The above embodiments of the present invention are provided for purposes of illustration and description. In addition, the embodiments of the present invention do not comprehensively and exhaustively cover the present invention and do not limit the present invention to the disclosed manners. Obviously, various modifications and variations are apparent to those skilled in the art to which the present invention pertains. This embodiment is selected and described in order to most easily explain the principle of the present invention and its applications. Thus, other technicians in this technical field can understand the present invention through various modified examples optimized for specific uses assumed to be various embodiments. The scope of the present invention is defined by the above claims and their equivalents.

Claims

1. A carrier for electrostatic image development, which has magnetic particles and a resin coating layer on the surface of the magnetic particles, has inorganic particles on the surface or contains inorganic particles in the resin coating layer, the inorganic particles contain Ti and any one of Ca, Sr, and Ba, the average roundness of the primary particles of the inorganic particles is 0.82 or more and 0.94 or less, The BET specific surface area of the magnetic particles is 0.12 m 2 / g or more and 0.24 m 2 / g or less.

2. The carrier for electrostatic image development according to claim 1, wherein the roundness of the inorganic particles at 84% cumulative exceeds 0.

92.

3. The carrier for electrostatic image development according to claim 1 or 2, wherein the ratio Mx / Mt of the total molar amount Mx of Ca, Sr, and Ba to the molar amount Mt of Ti in the inorganic particles is 0.65 or more and 0.90 or less.

4. The carrier for electrostatic image development according to any one of claims 1 to 3, wherein the fluidity of the carrier for electrostatic image development is 26 or more and 34 or less.

5. The carrier for electrostatic image development according to any one of claims 1 to 4, wherein the resin coating layer contains an acrylic resin having an aliphatic cyclic structure and an amino group.

6. The carrier for electrostatic image development according to claim 5, wherein the resin coating layer contains an acrylic resin having a structural unit with an aliphatic cyclic structure and a structural unit with an amino group.

7. The carrier for electrostatic image development according to any one of claims 1 to 6, wherein the average particle diameter of the carrier for electrostatic image development is 30 μm or more and 38 μm or less.

8. An electrostatic image developer, which contains the carrier for electrostatic image development according to any one of claims 1 to 7 and a toner.

9. A processing cartridge, which has a developing member that houses the electrostatic image developer according to claim 8 and develops an electrostatic image formed on the surface of an image holding body into a toner image, and the processing cartridge is detachably attached to an image forming apparatus.

10. An image forming method, which includes: a charging step of charging at least an image holding body; an exposure step of forming an electrostatic latent image on the surface of the image holding body; a developing step of developing the electrostatic latent image formed on the surface of the image holding body with an electrostatic image developer to form a toner image; a transfer step of transferring the toner image formed on the surface of the image holding body to the surface of a transfer body; and a fixing step of fixing the toner image, wherein the electrostatic image developer is the electrostatic image developer according to claim 8.

11. An image forming apparatus, which has: an image holding body; a charging member that charges the image holding body; an exposure member that exposes the charged image holding body to form an electrostatic latent image on the image holding body; a developing member that develops the electrostatic latent image with an electrostatic image developer to form a toner image; a transfer member that transfers the toner image from the image holding body to a transfer body; and a fixing member that fixes the toner image, wherein the electrostatic image developer is the electrostatic image developer according to claim 8.

Images