Toner for developing electrostatic images and image forming method

Abstract

To provide a toner for electrostatic charge image development that improves low temperature fixability, prevention of fogging, and durability, and prevents adherence of a fixed image.SOLUTION: A toner for electrostatic charge image development of the present invention is a toner for electrostatic charge image development that is formed of toner base particles containing at least a binder resin and magnetic substances, and an external additive. The binder resin contains a crystalline resin, and the external additive contains strontium titanate doped with a metal element other than titanium and strontium.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a toner for developing electrostatic images and an image forming method, and more particularly to a toner for developing electrostatic images having improved low-temperature fixability, fogging suppression and durability. [Background technology]

[0002] In image forming devices such as electrophotographic devices, electrostatic recording devices, and electrostatic printing devices, a method of forming a desired image by developing an electrostatic image formed on a photoconductor with a toner is widely practiced, and is applied to copiers, printers, facsimiles, and multifunction machines thereof. Such a toner is called a toner for developing an electrostatic image. Hereinafter, it will also be simply referred to as "toner".

[0003] For example, in an electrophotographic device using electrophotography, the surface of a photoconductor made of a photoconductive material is generally uniformly charged by various means, an electrostatic image is formed on the photoconductor, the electrostatic image is then developed with toner, the toner image is transferred to a recording material such as paper, and the toner image is fixed by heating or the like to obtain a copy.

[0004] Known developers used in image forming apparatuses include one-component developers that contain only toner, and two-component developers that contain a mixture of toner and carrier.

[0005] In recent years, image forming devices are required to be compact and energy-efficient in addition to high quality. For compactness, it is effective to use a single-component developer. For high quality, it is effective to form images using a single-component contact development method in which a toner carrier and an electrostatic image carrier are placed in contact with each other. However, in the single-component contact development method, a large pressure is applied to the contact area, so to obtain high-quality images, the toner must have high durability and transportability. For energy saving, it is effective to improve the low-temperature fixability of the toner.

[0006] Regarding the high transportability of toner, magnetic toners containing magnetic materials are known. However, since many magnetic materials generally have low electrical resistance, the charge of the magnetic toner is likely to decrease (charge decay) in the development process. Therefore, it is preferable to use an external additive with high resistance in order to prevent charge decay. Strontium titanate is known as such an external additive, but strontium titanate particles tend to have a cubic or rectangular shape due to their high crystallinity, and are therefore unlikely to adhere to the surface of the toner base particles described below.

[0007] Therefore, as a technology for giving strontium titanate a shape that makes it easier for it to adhere to the surface of toner base particles, Patent Document 1 discloses a technology in which strontium titanate is doped with a metal element other than titanium and strontium to reduce crystallinity, give it a rounded shape, and give it a small diameter and high circularity. This technology suppresses the charge decay of the toner, but magnetic toner has the problem of insufficient low-temperature fixing properties because the magnetic material penetrates between the binder resin and functions as a filler, and there is a demand for improved low-temperature fixing properties.

[0008] Patent Document 2 discloses a technique of introducing crystalline polyester into the binder resin, which is a component of the toner, as a method for improving the low-temperature fixability of the magnetic toner. However, the crystalline polyester seeps out onto the surface of the toner base particles in a high-temperature and high-humidity environment, softening the vicinity of the surface, which causes new magnetic material to be exposed on the surface, resulting in charge attenuation, fogging, and burying of external additives, leaving room for further improvement in the durability of the toner. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2019-28239 A [Patent Document 2] JP 2020-56920 A Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in consideration of the above problems and circumstances, and an object of the present invention is to provide a toner for developing electrostatic images and an image forming method which have improved low-temperature fixing properties, fogging suppression and durability. [Means for solving the problem]

[0011] In order to solve the above problems with magnetic toners, the present inventors have investigated the causes of the above problems, and have found that low-temperature fixing properties can be improved by incorporating a crystalline resin into the binder resin in the toner base particles, and that fogging can be suppressed and durability can be improved by incorporating strontium titanate doped with a metal element other than titanium and strontium into the external additive, which led to the present invention. That is, the above-mentioned problems of the present invention are solved by the following means.

[0012] 1. A toner for developing electrostatic images, which is composed of toner base particles containing at least a binder resin and a magnetic material, and an external additive, wherein the binder resin contains a crystalline resin, the content of the magnetic material is within a range of 30 to 50% by mass with respect to the total mass of the toner base particles, 1. A toner for developing electrostatic images, comprising: a toner for developing electrostatic images, the toner comprising: a strontium titanate doped with a metal element other than titanium or strontium;

[0013] 2. The toner for developing electrostatic images according to claim 1, wherein the strontium titanate is lanthanum-doped strontium titanate.

[0014] 3. The toner for developing electrostatic images according to item 1 or 2, wherein the number average primary particle diameter of the strontium titanate particles is within a range of 20 to 300 nm.

[0015] 4. The toner for developing electrostatic images according to any one of items 1 to 3, wherein the number average primary particle diameter of the strontium titanate particles is within a range of 20 to 100 nm.

[0016] 5. The toner for developing electrostatic images according to any one of items 1 to 4, wherein the average circularity of primary particles of the strontium titanate particles is within a range of 0.82 to 0.94.

[0017] 6. The toner for developing electrostatic images according to any one of items 1 to 5, wherein the crystalline resin is a crystalline polyester.

[0018] 7. A method for forming an image using a toner for developing an electrostatic image, comprising using the toner for developing an electrostatic image according to any one of items 1 to 6. Effect of the Invention

[0019] According to the above-mentioned means of the present invention, it is possible to provide a toner for developing electrostatic images having improved low-temperature fixing properties, fogging suppression and durability.

[0020] Although the mechanism by which the effects of the present invention are manifested or the mechanism by which the effects of the present invention are acted upon has not been clearly understood, it is speculated as follows.

[0021] Since most of the magnetic substances contained in magnetic toners have relatively low electrical resistance, if the magnetic substances are exposed on the surface of the toner, charge decay is likely to occur, and the charge amount of the magnetic toner is likely to decrease in the development process. Therefore, by attaching an external additive to the surface of the toner base particles containing the magnetic substance, the magnetic substances are unlikely to be exposed on the surface of the toner, and the decrease in the charge amount of the magnetic toner can be suppressed.

[0022] Since the external additive used needs to cover the surface of the toner base particles, it is preferable that the additive has sufficient adhesion to the toner base particles, and is preferably small in diameter and has a high circularity. Also, it is preferable that the additive has a high resistance in order to suppress a decrease in the charge amount of the magnetic toner.

[0023] On the other hand, by incorporating a crystalline resin into the binder resin in the toner base particles, the low-temperature fixing property can be improved. However, in a high-temperature and high-humidity environment, the crystalline resin seeps out onto the surface of the toner base particles, softening the surface vicinity, so that the magnetic material is newly exposed on the surface of the toner base particles, or the external additive is embedded in the toner base particles, making it impossible to suppress a decrease in the charge amount of the magnetic toner. Therefore, it is preferable that the external additive is one that is difficult to embed.

[0024] From this viewpoint, the object of the present invention can be achieved by including in the external additive strontium titanate doped with a metal element other than titanium and strontium. Strontium titanate will be described in detail below.

[0025] Strontium titanate is a composite oxide of strontium and titanium, and has a perovskite structure. The ions are regularly arranged to form a perovskite structure. 2+ Due to the large ionic radius of the ion, O 2- The ions are pushed apart, 2- Ti at the center of the octahedron made by ions 4+ Gaps form around the ions, and Ti 4+ The ions are displaced from the center. As a result, the electrical centers of the + and - ions do not coincide, resulting in ionic polarization.

[0026] Strontium titanate crystals are made up of stacked crystal structures, but the polarization directions are not all the same, but are individually different. However, when an external electric field is applied, these polarizations are aligned in the same direction, so that the entire strontium titanate crystal is largely polarized.

[0027] On the other hand, strontium titanate particles tend to assume a cubic or rectangular shape due to their high crystallinity, making them difficult to add to toner base particles. Therefore, by doping with a metal element other than titanium and strontium, the crystallinity can be reduced, resulting in particles with a small diameter and high circularity, making them easier to add to the outside. In addition, the reduced crystallinity causes the doped strontium titanate to be polarized even more.

[0028] The highly polarized doped strontium titanate, when externally added to the toner base particles, attracts, repels, and interacts with the magnetic material in the toner base particles. That is, when the magnetic material tries to be exposed on the surface of the toner base particles, it is repelled by the externally added strontium titanate and is pushed back into the toner base particles. Also, when the magnetic material is exposed on the surface of the toner base particles, the attracted strontium titanate covers the surface of the magnetic material, so that the exposure of the magnetic material is suppressed in the toner particles. That is, strontium titanate has a high crystallinity and therefore a high density compared to resins used as binder resins, and so is easily embedded in the toner base particles, but this embedding is suppressed by interaction with the magnetic material.

[0029] Furthermore, in reality, the surface of the toner base particle is uneven, and the attached strontium titanate particles tend to roll on the surface of the toner base particle and tend to gather in the recesses. These recesses are places where the magnetic material and the surface of the toner base particle are relatively close to each other, but the surface of the toner base particle is covered by the gathering of strontium titanate particles, so that the exposure of the magnetic material is suppressed in the toner particle.

[0030] In addition, the magnetic material improves the transportability of the toner and functions as a colorant, and therefore occupies a larger proportion of the toner base particles than general pigments, which means that the space in which the external additive can be embedded is relatively small, and the external additive is prevented from being embedded inside the toner base particles. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a developing device; [Diagram 2] FIG. 1 is a schematic cross-sectional view showing an example of an image forming apparatus using a single-component contact development system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The toner for developing an electrostatic image of the present invention is a toner for developing an electrostatic image, which is composed of toner base particles containing at least a binder resin and a magnetic material, and an external additive, wherein the binder resin contains a crystalline resin, the content of the magnetic material is within a range of 30 to 50% by mass with respect to the total mass of the toner base particles, The external additive contains strontium titanate doped with a metal element other than titanium and strontium. This feature is a technical feature common to or corresponding to the following embodiments.

[0033] In an embodiment of the present invention, from the viewpoints of ease of doping and ease of control of the particle shape of strontium titanate, the strontium titanate is preferably lanthanum-doped strontium titanate.

[0034] From the viewpoint of durability, the number average primary particle diameter of the strontium titanate particles is preferably within a range of 20 to 300 nm, more preferably within a range of 20 to 100 nm, and further, the average circularity of the primary particles of the strontium titanate particles is preferably within a range of 0.82 to 0.94.

[0035] From the viewpoint of low-temperature fixability, the crystalline resin is preferably a crystalline polyester.

[0036] The image forming method of the present invention is an image forming method using a toner for developing electrostatic images, and is characterized in that the toner for developing electrostatic images of the present invention is used. This makes it possible to form an image taking advantage of the characteristics of the toner for developing electrostatic images of the present invention.

[0037] The present invention, its components, and embodiments for carrying out the present invention will be described in detail below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after the symbol "to" are included as the lower and upper limits.

[0038] 1. Overview of the toner for developing electrostatic images of the present invention The toner for developing electrostatic images of the present invention (hereinafter, also simply referred to as "toner") is a toner for developing electrostatic images that is composed of toner base particles containing at least a binder resin and a magnetic material, and an external additive, and the binder resin contains a crystalline resin, the content of the magnetic material is within a range of 30 to 50% by mass with respect to the total mass of the toner base particles, The external additive contains strontium titanate doped with a metal element other than titanium and strontium.

[0039] The toner of the present invention includes toner particles having toner base particles and an external additive attached to the surface of the toner base particles. In this specification, "toner base particles" are those that constitute the base of "toner particles." The "toner base particles" according to the present invention contain at least a binder resin and a magnetic material, and may contain other components such as a colorant, a release agent (wax), and a charge control agent, as necessary. The "toner base particles" are called "toner particles" when an external additive is added. And, "toner" refers to an aggregate of toner particles.

[0040] [1.1 Toner base particles] <1.1.1 Magnetic material> The toner for developing electrostatic images of the present invention is characterized in that it contains a magnetic material in the toner base particles, and by containing the magnetic material in the toner base particles, it functions as a magnetic toner. The magnetic toner can be suitably used as it is as a one-component developer without being mixed with a carrier.

[0041] The magnetic material contained in the toner base particles according to the present invention attracts, repels, or interacts with the doped strontium titanate, which is an external additive. In addition, the magnetic material occupies a larger proportion of the toner base particles than general pigments, so the space in which the external additive can be embedded is relatively small. Therefore, the toner for developing electrostatic images according to the present invention contains a magnetic material, thereby suppressing the external additive from being embedded inside the toner base particles.

[0042] The term "magnetic body" refers to a material that is magnetized by the application of a magnetic field. Moreover, "magnetization" refers to the phenomenon in which a magnetic body is polarized and becomes a magnet when an external magnetic field is applied to the magnetic body. In the present invention, the magnetic body is preferably a ferromagnetic body, and a "ferromagnetic body" is a material with a large coercive force, that is, when magnetized by an external magnetic field, the magnetized state is maintained even when the external magnetic field is removed.

[0043] The magnetic material is not particularly limited, but examples thereof include iron oxides such as magnetite, maghemite, and ferrite, as well as simple metals such as iron, cobalt, and nickel, alloys of these metals with metals such as aluminum, copper, magnesium, tin, zinc, beryllium, calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures thereof.

[0044] The number average primary particle diameter of the magnetic material is preferably 0.50 μm or less, and is preferably within the range of 0.05 to 0.30 μm. The number average primary particle diameter can be measured using a transmission electron microscope. In the present invention, the term "primary particles" is used as a general term for crystals and strong agglomerates (called "aggregates") in which crystals share specific faces. The particle aggregates (called "agglomerates") formed by the aggregation of the primary particles are called "secondary particles."

[0045] Specifically, the toner particles to be observed are thoroughly dispersed in an epoxy resin, and then the resin is cured for two days in an atmosphere at 40°C to obtain a cured product. The cured product is cut into a thin slice sample using a microtome, and an image is taken with a transmission electron microscope (TEM) at a magnification of 10,000 to 40,000 times to measure the projected area of ​​100 primary particles of the magnetic material in the image. The equivalent diameter of a circle equal to the projected area is then taken as the particle diameter of the primary particles of the magnetic material, and the average value of the 100 particles is taken as the number-average primary particle diameter of the magnetic material.

[0046] As the magnetic properties of the magnetic material when 795.8 kA / m is applied, the coercive force (Hc) is preferably 1.6 to 12.0 kA / m. In addition, the magnetization strength (σs) is preferably 50 to 200 Am 2 / kg, and 50 to 100Am 2 On the other hand, the residual magnetization (σr) is preferably 2 to 20 Am 2 / kg is preferred.

[0047] The content of the magnetic material in the toner base particles is preferably within a range of 35 to 50% by mass, and more preferably within a range of 40 to 50% by mass, based on the total mass of the toner base particles. If the content of the magnetic material is within the above range, the magnetic attraction with the magnet roll in the developing sleeve becomes appropriate.

[0048] The content of the magnetic material in the toner base particles can be measured using a thermal analyzer TGA Q5000IR manufactured by PerkinElmer, Inc. The measurement method involves heating the magnetic toner from room temperature to 900°C at a heating rate of 25°C / min in a nitrogen atmosphere, and the weight loss from 100 to 750°C is taken as the weight of the components remaining after removing the magnetic material from the magnetic toner, and the remaining weight is taken as the weight of the magnetic material.

[0049] The magnetic material can be produced, for example, by the following method. An aqueous solution containing ferrous hydroxide is prepared by adding an equivalent or greater amount of alkali, such as sodium hydroxide, to an aqueous solution of ferrous salt. While maintaining the pH of the prepared aqueous solution at 7 or higher, air is blown in, and the aqueous solution is heated to 70°C or higher to carry out an oxidation reaction of the ferrous hydroxide, producing seed crystals that will become the cores of magnetic iron oxide.

[0050] Next, an aqueous solution containing about 1 equivalent of ferrous sulfate is added to the slurry containing the seed crystals, based on the amount of alkali added beforehand. The pH of the mixture is maintained at 5 to 10, and the reaction of ferrous hydroxide is allowed to proceed while blowing in air, and magnetic iron oxide is grown around the seed crystals as a core. At this time, the shape and magnetic properties of the magnetic material can be controlled by selecting any pH, reaction temperature, and stirring conditions. As the oxidation reaction proceeds, the pH of the mixture shifts to the acidic side, but it is preferable that the pH of the mixture is 5 or higher. The resulting mixture is filtered, washed, and dried by a standard method to obtain a magnetic material. Furthermore, the magnetic material may be subjected to a known surface treatment as necessary.

[0051] <1.1.2 Binder resin> The toner for developing electrostatic images of the present invention is characterized in that the binder resin in the toner base particles contains a crystalline resin. By including a crystalline resin in the binder resin in the toner base particles, low-temperature fixability can be improved.

[0052] The term "binding resin (also called "binder resin")" refers to a resin that is used as a medium or matrix (parent body) for dispersing internal additives (wax, charge control agent, pigment, etc.) and external additives (silica, titanium oxide, etc.) contained in toner particles, and has the function of adhering to a recording medium (e.g. paper) during the fixing process of a toner image.

[0053] The binder resin according to the present invention is not particularly limited, and conventionally known resins can be used. For example, polyester resins; polymers of styrene and its substitutes such as polyvinyltoluene; styrene-p-chlorostyrene copolymers, styrene-propylene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers, styrene-methyl acrylate copolymers, styrene-ethyl acrylate copolymers, styrene-butyl acrylate copolymers, styrene-octyl acrylate copolymers, styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate copolymers, styrene-butyl methacrylate copolymers, styrene-α-chloromethyl methacrylate copolymers, and styrene-acrylonitrile copolymers. copolymers such as styrene-based copolymers, styrene-vinyl methyl ketone copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers, styrene-maleic acid copolymers, and styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, epoxy resins, epoxy polyol resins, polyurethanes, polyamides, polyvinyl butyral, polyacrylic acid resins, rosin, modified rosin, terpene resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, etc. These resins may be used alone or in combination of two or more.

[0054] In addition, "the binder resin contains a crystalline resin" may mean that the binder resin contains the crystalline resin itself, or may contain a segment contained in another resin, such as a crystalline polyester polymer segment in a hybrid crystalline polyester resin or a crystalline polyester polymer segment in a hybrid amorphous polyester resin. In the present invention, from the viewpoint of low-temperature fixing property and heat-resistant storage property of the toner, it is preferable that the binder resin contains an amorphous resin in addition to the crystalline resin.

[0055] <1.1.2.1 Crystalline resin> In the present invention, the crystalline resin refers to a resin having a clear endothermic peak, not a stepwise endothermic change, in a differential calorimeter (DSC) measured differential calorimeter. Specifically, a clear endothermic peak means a peak whose half-width is within 15°C when measured at a heating rate of 10°C / min in DSC measurement. The DSC measurement is performed using a differential scanning calorimeter (PerkinElmer: Diamond DSC), and the melting points of indium and zinc are used to correct the temperature of the detector of this device, and the heat of fusion of indium is used to correct the heat quantity.

[0056] Such crystalline resins have high viscosity just before the melting point due to their high crystallinity, and the viscosity drops sharply around the melting point. Therefore, by including a crystalline resin in the binder resin, a toner having high storage stability in a high-temperature environment (heat-resistant storage stability) and high fixability can be obtained.

[0057] The melting point (Tm) of the crystalline resin is preferably within a range of 55 to 90°C, and more preferably within a range of 70 to 85°C, from the viewpoints of low-temperature fixability and hot offset resistance. The melting point of the crystalline resin can be controlled by the resin composition.

[0058] The melting point (Tm) is the temperature at the top of the endothermic peak, and can be measured by DSC. Specifically, the sample is sealed in an aluminum pan KINTO.B0143013 and set in the sample holder of a thermal analysis device Diamond DSC (PerkinElmer), and the temperature is changed in the order of heating, cooling, and heating. In the first heating, the temperature is raised from room temperature (25°C), and in the second heating, the temperature is raised from 0°C at a heating rate of 10°C / min to 150°C and held at 150°C for 5 minutes, and in the cooling, the temperature is lowered from 150°C to 0°C at a heating rate of 10°C / min and held at 0°C for 5 minutes. The temperature at the top of the endothermic peak in the endothermic curve obtained in the second heating is measured as the melting point.

[0059] From the viewpoint of low-temperature fixing property and heat-resistant storage property, the content of the crystalline resin in the toner base particles is preferably within a range of 1 to 40% by mass, and more preferably within a range of 5 to 30% by mass, based on the total mass of the toner base particles. If the content of the crystalline resin is 1% by mass or more, sufficient low-temperature fixing property is obtained, and if it is 40% by mass or less, sufficient thermal stability, stability against physical stress, and heat-resistant storage property as a toner are obtained.

[0060] From the viewpoint of low temperature fixability and heat resistance, the content of the crystalline resin is preferably within a range of 2 to 20% by mass, more preferably within a range of 5 to 20% by mass, and even more preferably within a range of 7 to 15% by mass, based on the total mass of the binder resin. If the content of the crystalline resin is 2% by mass or more, a sufficient plasticizing effect is obtained and low temperature fixability is more remarkable, and if it is 20% by mass or less, heat resistance is improved and sufficient thermal stability as a toner, stability against physical stress, and heat-resistant storage stability are obtained.

[0061] From the viewpoint of low-temperature fixing ability and gloss stability, the number average molecular weight (Mn) of the crystalline resin is preferably within the range of 3000 to 12500, and more preferably within the range of 4000 to 11000. Moreover, the weight average molecular weight (Mw) of the crystalline resin is preferably within the range of 10000 to 100000, more preferably within the range of 15000 to 80000, and even more preferably within the range of 20000 to 50000.

[0062] When Mw and Mn are within the above ranges, sharp melting properties are easily exhibited and fixing temperature is easily controlled. In addition, sufficient strength is obtained in the fixed image. Furthermore, in the production of the toner, the crystalline resin is not pulverized during stirring of the emulsion, and the glass transition temperature Tg of the toner is kept constant, so that the thermal stability of the toner is maintained. Mw and Mn can be determined from the molecular weight distribution measured by gel permeation chromatography (GPC) as follows.

[0063] (Method of measuring molecular weight of crystalline resin) The sample is added to tetrahydrofuran (THF) so that the concentration is 0.1 mg / mL, and then heated to 40°C to completely dissolve it, and then treated with a membrane filter with a pore size of 0.2 μm to prepare a sample solution (sample). Then, the measurement was performed under the following conditions. In detail, a GPC device HLC-8220GPC (manufactured by Tosoh Corporation) and a column "TSKgel Super H3000" (manufactured by Tosoh Corporation) are used, and THF is passed as a carrier solvent (eluent) at a flow rate of 0.6 mL / min while maintaining the column temperature at 40°C. 100 μL of the prepared sample solution is injected into the GPC device together with the carrier solvent, and the sample is detected using a differential refractive index detector (RI detector). Then, the molecular weight distribution of the sample is calculated using a calibration curve measured using 10 points of monodisperse polystyrene standard particles. In addition, in the data analysis, if a peak caused by the filter is confirmed, a baseline is set up to the peak, and the analyzed data is taken as the molecular weight of the sample.

[0064] Measurement model: Tosoh Corporation GPC device HLC-8220GPC Column: Tosoh Corporation "TSKgelSuperH3000" Eluent:THF Temperature: Column thermostat 40.0℃ Flow rate: 0.6ml / min Concentration: 0.1mg / mL (0.1wt / vol%) Calibration curve: Standard polystyrene sample manufactured by Tosoh Corporation Injection volume: 100μL Solubility: Completely dissolved (heated at 40℃) Pretreatment: Filtration through a 0.2μm filter Detector: Differential refractometer (RI)

[0065] The crystalline resin may be used alone or in combination of two or more. The type of crystalline resin is not particularly limited, and examples thereof include crystalline polyolefin resin, crystalline polydiene resin, crystalline polyester resin, crystalline polyamide resin, crystalline polyurethane resin, crystalline polyacetal resin, crystalline polyethylene terephthalate resin, crystalline polybutylene terephthalate resin, crystalline polyphenylene sulfide resin, crystalline polyether ether ketone resin, and crystalline polytetrafluoroethylene resin. Among these, crystalline polyester resin is preferred from the viewpoint of low-temperature fixability and gloss stability. The crystalline polyester resin melts during heat fixation and acts as a plasticizer for the amorphous resin, so that it can improve low-temperature fixability.

[0066] From the viewpoint of low-temperature fixability and heat-resistant storage stability, it is preferable to use a combination of a crystalline polyester resin and an amorphous resin as the binder resin, and it is more preferable to use a combination of a crystalline polyester resin and a vinyl resin.

[0067] [Crystalline polyester] Crystalline polyester (hereinafter also referred to as "crystalline polyester resin") refers to a resin that, among known polyester resins obtained by a polycondensation reaction between a divalent or higher carboxylic acid (polycarboxylic acid) and a divalent or higher alcohol (polyalcohol), shows a clear endothermic peak rather than a stepwise endothermic change in the above-mentioned differential scanning calorimetry (DSC).

[0068] In addition, the crystalline polyester resin melts during thermal fixing and acts as a plasticizer for the amorphous resin, thereby improving the low-temperature fixing property of the toner. The crystalline polyester resin may be used alone or in combination of two or more kinds.

[0069] The crystalline polyester resin is not particularly limited as long as it is as defined above. For example, a resin having a structure in which other components are copolymerized in the main chain of a crystalline polyester resin is also included in the crystalline polyester resin of the present invention as long as the resin shows the above-mentioned clear endothermic peak.

[0070] From the viewpoint of low-temperature fixability and gloss stability, the number average molecular weight (Mn) of the crystalline polyester resin is preferably within the range of 3000 to 12500, more preferably within the range of 4000 to 11000. The weight average molecular weight (Mw) of the crystalline polyester resin is preferably within the range of 10000 to 100000, more preferably within the range of 12000 to 80000, and even more preferably within the range of 14000 to 50000. Within the above ranges, the melting point of the toner obtained is within a suitable range, and the toner has excellent blocking resistance and low-temperature fixability. The number average molecular weight (Mn) and weight average molecular weight (Mw) can be measured by the above-mentioned gel permeation chromatography (GPC).

[0071] The acid value (AV) of the crystalline polyester resin is preferably 5 to 70 mgKOH / g. The acid value can be measured in accordance with the method described in JIS K2501:2003.

[0072] When the crystalline resin contained in the binder resin is a crystalline polyester resin, the content of the crystalline polyester resin is preferably within a range of 2 to 20% by mass, more preferably within a range of 5 to 20% by mass, and even more preferably within a range of 7 to 15% by mass, based on the total mass of the binder resin. If the content of the crystalline polyester resin is 2% by mass or more, the toner has excellent low-temperature fixing properties, and if it is 20% by mass or less, the toner has excellent heat resistance.

[0073] The crystalline polyester resin is produced from a polybasic carboxylic acid component and a polyhydric alcohol component. The valence of each of the polybasic carboxylic acid component and the polyhydric alcohol component is preferably 2 to 3, and particularly preferably 2.

[0074] (Polycarboxylic Acid) The polycarboxylic acid is a compound containing two or more carboxyl groups in one molecule. An example of the polycarboxylic acid is a dicarboxylic acid. The dicarboxylic acid may be used alone or in combination of two or more. The dicarboxylic acid is preferably an aliphatic dicarboxylic acid, and may further contain an aromatic dicarboxylic acid. The aliphatic dicarboxylic acid is preferably a straight-chain type from the viewpoint of increasing the crystallinity of the crystalline polyester resin.

[0075] Examples of the aliphatic dicarboxylic acid include saturated aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid (hexanedioic acid), pimelic acid, suberic acid (octanedioic acid), azelaic acid, sebacic acid (decanedioic acid), n-dodecyl succinic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid (dodecanedioic acid), 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid (tetradecanedioic acid), 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, and 1,18-octadecanedicarboxylic acid, lower alkyl esters thereof, and acid anhydrides thereof. Among these, from the viewpoint of compatibility between low-temperature fixability and transferability, aliphatic dicarboxylic acids having 6 to 16 carbon atoms are preferred, and aliphatic dicarboxylic acids having 10 to 14 carbon atoms are more preferred.

[0076] Examples of the aromatic dicarboxylic acid include phthalic acid, terephthalic acid, isophthalic acid, orthophthalic acid, t-butylisophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid. Among them, terephthalic acid, isophthalic acid, and t-butylisophthalic acid are preferred from the viewpoints of availability and ease of emulsification.

[0077] In addition to the above, examples of the polyvalent carboxylic acid include alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, trivalent or higher polyvalent carboxylic acids such as trimellitic acid and pyromellitic acid, and anhydrides or alkyl esters having 1 to 3 carbon atoms of these carboxylic acid compounds.

[0078] The polyvalent carboxylic acids may be used alone or in combination of two or more kinds.

[0079] From the viewpoint of the crystallinity of the crystalline polyester resin, the content of the constituent units derived from aliphatic dicarboxylic acids relative to the constituent units derived from dicarboxylic acids is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 100 mol%.

[0080] (Polyhydric alcohol) A polyhydric alcohol is a compound containing two or more hydroxyl groups in one molecule. An example of the polyhydric alcohol component is a diol. The diol may be used alone or in combination of two or more. The diol is preferably an aliphatic diol, and may further contain other diols. The aliphatic diol is preferably a straight-chain type from the viewpoint of increasing the crystallinity of the crystalline polyester resin.

[0081] Examples of the aliphatic diol include ethylene glycol, propylene glycol (1,2-propanediol), 1,3-propanediol, neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,20-eicosanediol. Among them, from the viewpoint of compatibility between low-temperature fixing property and transferability, aliphatic diols having 2 to 20 carbon atoms are preferred, and aliphatic diols having 4 to 12 carbon atoms are more preferred.

[0082] Examples of the other diols include diols having a double bond and diols having a sulfonic acid group.Specific examples of the diols having a double bond include 1,4-butenediol, 2-butene-1,4-diol, 3-butene-1,6-diol, and 4-butene-1,8-diol.

[0083] Examples of trihydric or higher polyhydric alcohols include glycerin, pentaerythritol, trimethylolpropane, and sorbitol.

[0084] The polyhydric alcohols may be used alone or in combination of two or more kinds.

[0085] From the viewpoints of low-temperature fixability and gloss stability, the content of the aliphatic diol-derived structural units relative to the diol-derived structural units is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, and particularly preferably 100 mol %.

[0086] The ratio of diol to dicarboxylic acid in the monomers constituting the crystalline polyester resin, i.e., the equivalent ratio [-OH] / [-COOH] of the hydroxy group [-OH] of the diol to the carboxy group [-COOH] of the dicarboxylic acid, is preferably within the range of 2.0 / 1.0 to 1.0 / 2.0, more preferably within the range of 1.5 / 1.0 to 1.0 / 1.5, and even more preferably within the range of 1.3 / 1.0 to 1.0 / 1.3.

[0087] The monomer constituting the crystalline polyester resin preferably contains 50% by mass or more of a linear aliphatic monomer, more preferably 80% by mass or more. When a linear aliphatic monomer is used, the crystallinity of the crystalline polyester resin is high, and the melting point (the temperature at the top of the endothermic peak) is often high. When a branched aliphatic monomer is used, the crystallinity is low, and the melting point is often low. Therefore, it is preferable to use a linear aliphatic monomer as the monomer.

[0088] The crystalline polyester resin can be synthesized by polycondensing (esterifying) the above-mentioned polyvalent carboxylic acid and polyhydric alcohol using a known esterification catalyst.

[0089] The esterification catalyst may be used alone or in combination of two or more. Examples of the esterification catalyst include alkali metal compounds such as sodium and lithium, compounds containing Group 2 elements such as magnesium and calcium, metal compounds such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium, and germanium, phosphorous compounds, phosphoric acid compounds, and amine compounds.

[0090] Specifically, examples of tin compounds include dibutyltin oxide, tin octoate, tin dioctoate, and salts thereof. Examples of titanium compounds include titanium alkoxides such as tetra-normal-butyl titanate, tetraisopropyl titanate, tetramethyl titanate, and tetrastearyl titanate; titanium acylates such as polyhydroxytitanium stearate; and titanium chelates such as titanium tetraacetylacetonate, titanium lactate, and titanium triethanolamine. Examples of germanium compounds include germanium dioxide, and examples of aluminum compounds include oxides such as polyaluminum hydroxide, aluminum alkoxides, and tributylaluminate.

[0091] The polymerization temperature for the crystalline polyester resin is preferably within a range of 150 to 250° C. The polymerization time is preferably within a range of 0.5 to 10 hours. During the polymerization, the pressure in the reaction system may be reduced as necessary.

[0092] The crystallinity and heat of fusion of the crystalline polyester resin can be controlled by selecting the structure and constituent monomer of the crystalline polyester resin. From the viewpoint of adjusting the crystallinity of the crystalline polyester resin to a range preferred for fixing, the crystalline polyester resin is preferably a hybrid crystalline polyester resin described below. The hybrid crystalline polyester resin may be used alone or in combination of two or more kinds. The hybrid crystalline polyester resin may replace the entire amount of the crystalline polyester resin or may replace a part of the crystalline polyester resin.

[0093] [Hybrid crystalline polyester resin] The crystalline resin according to the present invention is preferably a crystalline polyester resin, and from the viewpoint of low-temperature fixability, the crystalline polyester resin is preferably a hybrid crystalline polyester resin containing a crystalline polyester resin structure and an amorphous resin structure. Since the hybrid crystalline polyester resin contains an amorphous resin structure, it has high compatibility with the amorphous resin and can maintain a more finely dispersed state in the binder resin, and since it contains a crystalline polyester resin structure, the sharp melting property of the crystalline resin is more exhibited during fixing, improving low-temperature fixability. In addition, when the toner base particles have a core-shell structure, it is preferable to include a hybrid crystalline polyester resin in the core portion from the viewpoint of making it difficult for the crystalline polyester resin to be exposed on the surface of the toner base particles.

[0094] The hybrid crystalline polyester resin is a resin having a structure in which a crystalline polyester polymerized segment and an amorphous polymerized segment are chemically bonded. The crystalline polyester polymerized segment means a portion derived from a crystalline polyester resin. That is, it means a molecular chain having the same chemical structure as the molecular chain constituting the crystalline polyester resin described above. The amorphous polymerized segment means a portion derived from an amorphous resin. That is, it means a molecular chain having the same chemical structure as the molecular chain constituting the amorphous resin described below.

[0095] The weight average molecular weight (Mw) of the hybrid crystalline polyester resin is preferably within the range of 20,000 to 50,000. By setting Mw to 50,000 or less, sufficient low-temperature fixing property can be obtained. On the other hand, by setting Mw to 20,000 or more, excessive progress of compatibility between the hybrid resin and the amorphous resin during toner storage can be suppressed, and image defects due to fusion between toner particles can be suppressed. The weight average molecular weight can be measured by the above-mentioned method for measuring the molecular weight of the crystalline resin.

[0096] For the same reason, the number average molecular weight (Mn) of the hybrid crystalline polyester resin is preferably within the range of 3,000 to 12,500, and more preferably within the range of 4,000 to 11,000.

[0097] When the crystalline resin contains a hybrid crystalline polyester resin, the content of the hybrid crystalline polyester resin is preferably within a range of 2 to 20% by mass, more preferably within a range of 5 to 20% by mass, and even more preferably within a range of 7 to 15% by mass, based on the total mass of the binder resin. When the content of the hybrid crystalline polyester resin is 2% by mass or more, the low-temperature fixing property is excellent, and when it is 20% by mass or less, the heat resistance is excellent.

[0098] The structure of the chemical bond is not particularly limited and may be a block copolymer or a graft copolymer, but is preferably a structure in which the crystalline polyester polymerized segment is grafted to the amorphous polymerized segment as the main chain. That is, the hybrid crystalline polyester resin is preferably a graft copolymer having an amorphous polymerized segment as the main chain and a crystalline polyester polymerized segment as a side chain.

[0099] The hybrid crystalline polyester resin having such a structure will be described below.

[0100] (Crystalline polyester polymer segment) The crystalline polyester polymer segment refers to a portion derived from a crystalline polyester resin, that is, a molecular chain having the same chemical structure as that constituting the crystalline polyester resin.

[0101] The crystalline polyester polymerized segment is synonymous with the crystalline polyester resin described above, and is a portion derived from a known polyester resin obtained by polycondensation reaction of a polycarboxylic acid and a polyhydric alcohol. The crystalline polyester polymerized segment can be synthesized from a polycarboxylic acid and a polyhydric alcohol in the same manner as the crystalline polyester resin described above. Note that the polycarboxylic acid component and the polyhydric alcohol component constituting the crystalline polyester polymerized segment are the same as those described in the "polycarboxylic acid" and "polyhydric alcohol" items in the crystalline polyester resin described above, and therefore will not be described here.

[0102] The content of the crystalline polyester polymer segment is preferably within a range of 80 to 98% by mass, more preferably within a range of 90 to 95% by mass, based on the total mass of the hybrid crystalline polyester resin. By being within the above range, sufficient crystallinity can be imparted to the hybrid crystalline polyester resin. The components and contents of each segment in the hybrid crystalline polyester resin (or toner particles) can be identified by utilizing known analytical methods such as nuclear magnetic resonance (NMR) measurement and methylation reaction pyrolysis gas chromatography / mass spectrometry (Py-GC / MS).

[0103] The crystalline polyester polymerized segment preferably contains a monomer having an unsaturated bond from the viewpoint of introducing a chemical bonding site with the amorphous polymerized segment into the segment. The monomer having an unsaturated bond is, for example, a polyvalent carboxylic acid and a polyhydric alcohol having a double bond, and examples thereof include polyvalent carboxylic acids such as methylene succinic acid, fumaric acid, maleic acid, 3-hexenedioic acid, and 3-octenedioic acid; and polyhydric alcohols such as 2-butene-1,4-diol, 3-butene-1,6-diol, and 4-butene-1,8-diol. The content of the constituent unit derived from the monomer having an unsaturated bond in the crystalline polyester polymerized segment is preferably within a range of 0.5 to 20% by mass with respect to the total mass of the crystalline polyester polymerized segment.

[0104] The hybrid crystalline polyester resin may further include a functional group such as a sulfonic acid group, a carboxy group, or a urethane group. The functional group may be introduced into the crystalline polyester polymer segment or into the amorphous polymer segment.

[0105] (Amorphous polymerized segment) The amorphous polymerized segment refers to a portion derived from an amorphous resin. In other words, it refers to a molecular chain having the same chemical structure as that constituting the amorphous resin. When the binder resin according to the present invention contains an amorphous resin, the amorphous polymerized segment enhances the compatibility between the hybrid crystalline polyester resin and the amorphous resin. Therefore, the hybrid crystalline resin is easily incorporated into the amorphous resin, and the charging uniformity of the toner is further improved. The components and the content of the amorphous polymerized segment in the hybrid crystalline polyester resin (or toner particles) can be identified by using known analytical methods such as nuclear magnetic resonance (NMR) measurement and methylation reaction pyrolysis gas chromatography / mass spectrometry (Py-GC / MS).

[0106] The amorphous polymer segment is a polymer segment that has no melting point and a relatively high glass transition temperature (Tg) when a differential scanning calorimetry (DSC) is performed on a resin having the same chemical structure and molecular weight. The amorphous polymer segment preferably has a glass transition temperature (Tg) in the first heating process of DSC in the same range as the amorphous resin, and more preferably has a glass transition temperature (Tg) in the range of 30 to 80°C, and more preferably in the range of 40 to 65°C. The glass transition temperature (Tg) can be measured in the same manner as the Tg of the amorphous resin.

[0107] The amorphous polymer segment is preferably composed of the same type of resin as the amorphous resin (e.g., vinyl resin) contained in the binder resin, from the viewpoint of increasing compatibility with the binder resin and increasing the charging uniformity of the toner. By adopting such a form, the compatibility between the hybrid crystalline polyester resin and the amorphous resin is further improved. The "same type of resin" means resins having characteristic chemical bonds in the repeating units.

[0108] The "characteristic chemical bonds" are based on the "polymer classification" described in the National Institute for Materials Science (NIMS) Materials Database (http: / / polymer.nims.go.jp / PoLyInfo / guide / jp / term_polymer.html). In other words, the chemical bonds that make up polymers classified into a total of 22 types, including polyacrylic, polyamide, polyanhydride, polycarbonate, polydienes, polyesters, polyhaloolefins, polyimides, polyimines, polyketones, polyolefins, polyethers, polyphenylenes, polyphosphazenes, polysiloxanes, polystyrenes, polysulfides, polysulfones, polyurethanes, polyureas, polyvinyls, and other polymers, are called "characteristic chemical bonds."

[0109] In addition, when the resin is a copolymer, "same type of resin" means resins that have a common characteristic chemical bond when the monomer species having the above-mentioned chemical bond is used as a constituent unit in the chemical structure of a plurality of monomer species that constitute the copolymer. Therefore, even if the properties exhibited by the resins themselves are different from each other or the molar component ratios of the monomer species that constitute the copolymer are different from each other, they are considered to be the same type of resins as long as they have a common characteristic chemical bond.

[0110] For example, a resin (or a polymerized segment) formed by styrene, butyl acrylate, and acrylic acid and a resin (or a polymerized segment) formed by styrene, butyl acrylate, and methacrylic acid have at least a chemical bond constituting polyacrylic, and therefore, they are the same type of resin. For further example, a resin (or a polymerized segment) formed by styrene, butyl acrylate, and acrylic acid and a resin (or a polymerized segment) formed by styrene, butyl acrylate, acrylic acid, terephthalic acid, and fumaric acid have at least a chemical bond constituting polyacrylic as a common chemical bond. Therefore, they are the same type of resin.

[0111] From the viewpoint of introducing a chemical bonding site with the crystalline polyester polymer segment into the amorphous polymer segment, the amorphous polymer segment preferably contains an amphoteric compound, which will be described later, in the monomer. The content of the constitutional unit derived from the amphoteric compound is preferably within a range of 0.5 to 20% by mass with respect to the total mass of the amorphous polymer segment.

[0112] From the viewpoint of imparting sufficient crystallinity to the hybrid crystalline polyester resin, the content of the amorphous polymer segment is preferably within the range of 2 to 20 mass%, more preferably within the range of 3 to 15 mass%, even more preferably within the range of 5 to 10 mass%, and particularly preferably within the range of 7 to 9 mass%, relative to the total mass of the hybrid crystalline polyester resin.

[0113] The resin component constituting the amorphous polymerized segment is not particularly limited, and examples thereof include a vinyl polymerized segment, a urethane polymerized segment, a urea polymerized segment, etc. Among these, from the viewpoint of thermoplasticity, a vinyl polymerized segment is preferred.

[0114] In addition, when the vinyl polymerization segment is used, it is preferable to use a vinyl resin as the amorphous resin in the binder resin, and moreover, it is preferable that the vinyl resin is contained in the binder resin in the largest proportion. This increases the compatibility between the vinyl polymerization segment and the vinyl resin, and the hybrid crystalline polyester resin can be kept in a more finely dispersed state in the binder resin, and the sharp melting property of the crystalline resin is more likely to be exhibited during fixing. The vinyl polymerization segment can be synthesized in the same manner as the vinyl resin.

[0115] The vinyl polymerized segment is not particularly limited as long as it is a polymerized vinyl compound, and examples thereof include an acrylic acid ester polymerized segment, a styrene-acrylic acid ester polymerized segment, an ethylene-vinyl acetate polymerized segment, etc. These may be used alone or in combination of two or more.

[0116] Among the above vinyl polymerized segments, in consideration of the plasticity during thermal fixing, the styrene-acrylic ester polymerized segment (also simply referred to as "styrene-acrylic polymerized segment") is preferred. Therefore, the styrene-acrylic polymerized segment as an amorphous polymerized segment will be described below.

[0117] (styrene-acrylic polymerized segment) The styrene-acrylic polymerization segment is formed by addition polymerization of at least a styrene monomer and a (meth)acrylic acid ester monomer. The styrene monomer referred to here includes styrene represented by the structural formula CH2=CH-C6H5, as well as a structure having a known side chain or functional group in the styrene structure. The (meth)acrylic acid ester monomer referred to here includes acrylic acid ester compounds represented by CH2=CHCOOR (R is an alkyl group) and methacrylic acid ester compounds, as well as ester compounds having known side chains or functional groups in the structure of acrylic acid ester derivatives and methacrylic acid ester derivatives.

[0118] Specific examples of styrene monomers and (meth)acrylic acid ester monomers capable of forming the styrene-acrylic polymerization segment are shown below, but those usable for forming the styrene-acrylic polymerization segment used in the present invention are not limited to the following.

[0119] (styrene monomer) Specific examples of styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, etc. These styrene monomers may be used alone or in combination of two or more.

[0120] ((Meth)acrylic acid ester monomer) Specific examples of (meth)acrylic acid ester monomers include acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, and phenyl acrylate; and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate, and dimethylaminoethyl methacrylate. Among these, it is preferable to use a long-chain acrylic acid ester monomer. Specifically, methyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate are preferred.

[0121] In this specification, the term "(meth)acrylic acid ester monomer" collectively refers to "acrylic acid ester monomer" and "methacrylic acid ester monomer", for example, "methyl (meth)acrylate" collectively refers to "methyl acrylate" and "methyl methacrylate".

[0122] These acrylic acid ester monomers or methacrylic acid ester monomers may be used alone or in combination of two or more. That is, it is possible to form a copolymer using a styrene monomer and two or more acrylic acid ester monomers, to form a copolymer using a styrene monomer and two or more methacrylic acid ester monomers, or to form a copolymer using a styrene monomer in combination with an acrylic acid ester monomer and a methacrylic acid ester monomer.

[0123] From the viewpoint of plasticity, the content of the structural units derived from the styrene monomer in the styrene-acrylic polymerization segment is preferably within a range of 40 to 90% by mass relative to the total mass of the styrene-acrylic polymerization segment. From the same viewpoint, the content of the structural units derived from the (meth)acrylic acid ester monomer in the styrene-acrylic polymerization segment is preferably within a range of 10 to 60% by mass relative to the total mass of the styrene-acrylic polymerization segment.

[0124] Furthermore, the styrene-acrylic polymerization segment is preferably formed by addition polymerization of a compound for chemically bonding to the crystalline polyester polymerization segment in addition to the styrene monomer and (meth)acrylic acid ester monomer. Specifically, it is preferable to use a compound that forms an ester bond with the hydroxy group [-OH] derived from the polyhydric alcohol component or the carboxy group [-COOH] derived from the polycarboxylic acid component contained in the crystalline polyester polymerization segment. Therefore, the styrene-acrylic polymerization segment is preferably formed by further polymerizing a compound that can be addition polymerized with the styrene monomer and (meth)acrylic acid ester monomer and has a carboxy group [-COOH] or a hydroxy group [-OH].

[0125] Examples of such compounds include compounds having a carboxy group, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, cinnamic acid, fumaric acid, maleic acid monoalkyl esters, and itaconic acid monoalkyl esters; and compounds having a hydroxy group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and polyethylene glycol mono(meth)acrylate.

[0126] The content of the constituent units derived from the above compounds in the styrene-acrylic polymerization segment is preferably within a range of 0.5 to 20 mass % relative to the total mass of the styrene-acrylic polymerization segment, from the viewpoint of introducing chemical bonding sites with the above crystalline polyester polymerization segment into the styrene-acrylic polymerization segment.

[0127] The method for forming the styrene-acrylic polymerized segment is not particularly limited, and examples thereof include a method of polymerizing monomers using a known oil-soluble or water-soluble polymerization initiator. Specific examples of the oil-soluble polymerization initiator include the following azo or diazo polymerization initiators and peroxide polymerization initiators.

[0128] (Azo or diazo polymerization initiator) Examples of the azo or diazo polymerization initiator include 2,2'-azobis-(2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, and azobisisobutyronitrile.

[0129] (Peroxide-based polymerization initiator) Examples of the peroxide polymerization initiator include benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxypivalate, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide, 2,2-bis-(4,4-t-butylperoxycyclohexyl)propane, and tris-(t-butylperoxy)triazine.

[0130] When resin particles are formed by emulsion polymerization, a water-soluble radical polymerization initiator can be used, such as persulfates such as potassium persulfate and ammonium persulfate, azobisaminodipropane acetate, azobiscyanovaleric acid and its salts, and hydrogen peroxide.

[0131] (Method for producing hybrid crystalline polyester resin) The method for producing the hybrid crystalline polyester resin is not particularly limited as long as it is a method capable of forming a polymer having a structure in which the above-mentioned crystalline polyester polymerized segment and the amorphous polymerized segment are chemically bonded. As a specific method for producing the hybrid crystalline polyester resin, for example, it can be produced by the following first to third production methods.

[0132] (First manufacturing method) The first production method is a method for producing a hybrid crystalline polyester resin by carrying out a polymerization reaction for synthesizing a crystalline polyester polymer segment in the presence of a pre-synthesized amorphous polymer segment.

[0133] (Second manufacturing method) The second production method is a method in which a crystalline polyester polymer segment and an amorphous polymer segment are formed in advance, and then these are bonded to produce a hybrid crystalline polyester resin.

[0134] (Third manufacturing method) The third production method is a method of producing a hybrid crystalline polyester resin by carrying out a polymerization reaction to synthesize an amorphous polymer segment in the presence of a crystalline polyester polymer segment.

[0135] Among the above first to third manufacturing methods, the first manufacturing method is preferred because it is easy to synthesize a hybrid crystalline polyester resin having a structure in which a crystalline polyester polymer chain (crystalline polyester resin chain) is grafted to an amorphous polymer chain (amorphous resin chain) and because it can simplify the production process. The first manufacturing method is preferred because the orientation of the crystalline polyester polymer segment is easily uniform because the amorphous polymer segment is formed in advance and then the crystalline polyester polymer segment is bonded to the amorphous polymer segment. Therefore, it is preferred from the viewpoint of easy synthesis of a hybrid crystalline polyester resin suitable for the toner of the present invention.

[0136] <1.1.2.2 Amorphous resin> The toner base particles according to the present invention preferably contain, as a binder resin, an amorphous resin in addition to a crystalline resin. The amorphous resin is a resin that does not have the above-mentioned "crystallinity". By including the amorphous resin in the toner base particles, the crystalline resin and the amorphous resin become compatible with each other during heat fixing, thereby improving the low-temperature fixing property of the toner.

[0137] In other words, an amorphous resin is a resin that does not have a melting point (i.e., does not have the aforementioned clear endothermic peak upon heating) and has a relatively high glass transition temperature (Tg) in the endothermic curve obtained when differential scanning calorimetry (DSC) is performed.

[0138] In the present invention, the Tg of the amorphous resin is preferably within the range of 35 to 80°C, and more preferably within the range of 45 to 65°C.

[0139] From the viewpoint of achieving both low-temperature fixing property, hot offset resistance and heat resistance, it is preferable that the toner base particles have a core-shell structure. When the core portion of the core-shell structure contains a particle of a three-layer structure of a release agent (wax)-containing amorphous resin (for example, a release agent-containing amorphous vinyl resin), the Tg of the amorphous resin constituting the outermost layer of the particle is preferably within the range of 55 to 65°C.

[0140] The glass transition temperature can be measured according to the method (DSC method) specified in ASTM D3418-82. For the measurement, a DSC-7 differential scanning calorimeter (manufactured by PerkinElmer), a TAC7 / DX thermal analyzer controller (manufactured by PerkinElmer), or the like can be used.

[0141] From the viewpoint of plasticity, the weight average molecular weight (Mw) of the amorphous resin is preferably within a range of 20,000 to 150,000, and more preferably within a range of 25,000 to 130,000. From the viewpoint of plasticity, the number average molecular weight (Mn) of the amorphous resin is preferably within a range of 5,000 to 150,000, and more preferably within a range of 8,000 to 70,000. The molecular weight of the amorphous resin can be measured in the same manner as the method for measuring the molecular weight of the crystalline resin described above.

[0142] The mass ratio of the amorphous resin to the crystalline resin (amorphous resin / crystalline resin) is preferably within a range of 98 / 2 to 80 / 20, more preferably within a range of 95 / 5 to 80 / 20. By having the mass ratio within the above range, the crystalline resin is not exposed on the surface of the toner base particles, or even if it is exposed, the amount of the crystalline resin is extremely small, and an amount of the crystalline resin sufficient to achieve low-temperature fixability can be introduced into the toner particles.

[0143] The amorphous resin is preferably used as a binder resin together with the crystalline resin to constitute the toner base particles. By including the amorphous resin, appropriate fixed image strength and image gloss can be obtained, and good charging characteristics can be imparted even in an environment of varying temperature and humidity.

[0144] Furthermore, when the toner base particles according to the present invention have a core-shell structure, from the viewpoints of controllability of the dispersion state in the toner base particles and charging characteristics, it is preferable that an amorphous vinyl resin and a crystalline polyester resin form the core portion, and a hybrid amorphous polyester resin form the shell layer.

[0145] The amorphous resin may be used alone or in combination of two or more. Examples of the amorphous resin include vinyl resin, urethane resin, urea resin, and amorphous polyester resin such as styrene-acrylic modified polyester resin. From the viewpoint of thermoplasticity, the amorphous resin preferably contains an amorphous vinyl resin (also simply referred to as vinyl resin). These amorphous resins can be obtained by known synthesis methods or as commercially available products.

[0146] The vinyl resin will be described below.

[0147] (Vinyl resin) The binder resin according to the present invention is preferably mainly composed of a vinyl resin. By using a vinyl resin as the main component, it is easy to adjust the compatibility / immiscibility between the crystalline resin and the amorphous resin, and the crystalline polyester resin can be kept in a finely dispersed state in the binder resin, particularly in the vinyl resin as the main component, so that the sharp melting property of the crystalline polyester resin is more effectively exhibited during fixing.

[0148] The content of the vinyl resin is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more, based on the total mass of the binder resin. By using the vinyl resin as the main component (50% by mass or more based on the total mass of the binder resin), it is easy to adjust the compatibility with the crystalline resin, and low-temperature fixability and heat resistance can be both achieved. The upper limit of the content of the vinyl resin is not particularly limited, but is preferably 98% by mass or less, more preferably 95% by mass or less, and even more preferably 93% by mass or less, based on the total mass of the binder resin.

[0149] The binder resin according to the present invention preferably contains a vinyl resin as a main component and further contains an amorphous polyester resin, because the inclusion of the amorphous polyester resin makes it easier to adjust the compatibility with the crystalline resin.

[0150] In addition, when the toner base particles have a core-shell structure, since the amorphous polyester resin has better heat resistance than the vinyl resin, the toner can have both high heat resistance and low-temperature fixability by providing a shell layer using the amorphous polyester resin. From this viewpoint, the content of the amorphous polyester resin is preferably within a range of 2 to 20% by mass, more preferably within a range of 3 to 18% by mass, and even more preferably within a range of 4 to 15% by mass, based on the total mass of the binder resin.

[0151] In the present invention, the vinyl resin is, for example, a polymer of a vinyl compound, and examples thereof include acrylic acid ester resin, styrene-acrylic acid ester resin, ethylene-vinyl acetate resin, etc. These may be used alone or in combination of two or more. Among them, styrene-acrylic acid ester resin (styrene-acrylic resin) is preferable from the viewpoint of plasticity during thermal fixing. The styrene monomer and (meth)acrylic acid ester monomer used in the styrene-acrylic resin may be the same as those described in the above-mentioned items "styrene monomer" and "(meth)acrylic acid ester monomer".

[0152] Styrene-acrylic resin is formed by addition polymerization of at least a styrene monomer and a (meth)acrylic acid ester monomer. The styrene monomer includes styrene represented by the structural formula CH2=CH-C6H5, as well as styrene derivatives having known side chains or functional groups in the styrene structure.

[0153] In addition, the (meth)acrylic acid ester monomer includes acrylic acid esters and methacrylic acid esters represented by CH(R1)=CHCOOR2 (R1 represents a hydrogen atom or a methyl group, and R2 represents an alkyl group having 1 to 24 carbon atoms), as well as acrylic acid ester derivatives and methacrylic acid ester derivatives having known side chains or functional groups in the structure of these esters.

[0154] Examples of styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, and pn-dodecylstyrene.

[0155] Examples of the (meth)acrylic acid ester monomer include acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, and phenyl acrylate; and methacrylic acid ester monomers such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate, and dimethylaminoethyl methacrylate.

[0156] In this specification, the term "(meth)acrylic acid ester monomer" is a general term for "acrylic acid ester monomer" and "methacrylic acid ester monomer" and means one or both of them. For example, "methyl (meth)acrylate" means one or both of "methyl acrylate" and "methyl methacrylate".

[0157] The (meth)acrylic acid ester monomer may be used alone or in combination of two or more. For example, it is possible to form a copolymer using a styrene monomer and two or more acrylic acid ester monomers, to form a copolymer using a styrene monomer and two or more methacrylic acid ester monomers, or to form a copolymer using a styrene monomer, an acrylic acid ester monomer, and a methacrylic acid ester monomer in combination.

[0158] From the viewpoint of plasticity, the content of the structural units derived from the styrene monomer is preferably within a range of 40 to 90% by mass relative to the total mass of the amorphous resin, and the content of the structural units derived from the (meth)acrylic acid ester monomer is preferably within a range of 10 to 60% by mass relative to the total mass of the amorphous resin.

[0159] The amorphous resin may further contain a constituent unit derived from a monomer other than the above-mentioned styrene monomer and (meth)acrylic acid ester monomer. The other monomer is preferably a compound that forms an ester bond with a hydroxy group [-OH] derived from a polyhydric alcohol or a carboxy group [-COOH] derived from a polycarboxylic acid. In other words, the amorphous resin is preferably a polymer that can be addition polymerized with the above-mentioned styrene monomer and (meth)acrylic acid ester monomer, and is further polymerized with an amphoteric compound (a compound having a carboxy group or a hydroxy group).

[0160] The "amphoteric compound" in the present invention is a monomer that bonds a crystalline polyester polymerized segment and an amorphous polymerized segment, and has in its molecule a substituent such as a hydroxy group, a carboxy group, an epoxy group, a primary amino group, a secondary amino group, etc., that can react with the crystalline polyester polymerized segment, and an ethylenically unsaturated group that can react with the amorphous polymerized segment. Among these, vinyl carboxylic acid having a hydroxy group or a carboxy group and an ethylenically unsaturated group is preferred.

[0161] Examples of the amphoteric compound include compounds having a carboxy group, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, cinnamic acid, fumaric acid, maleic acid monoalkyl ester, and itaconic acid monoalkyl ester; and compounds having a hydroxy group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and polyethylene glycol mono(meth)acrylate.

[0162] The content of the constitutional units derived from the amphoteric compound is preferably within a range of 0.5 to 20% by mass relative to the total mass of the amorphous resin.

[0163] The styrene-acrylic resin can be synthesized by a method of polymerizing monomers using a known oil-soluble or water-soluble polymerization initiator. Examples of oil-soluble polymerization initiators include azo- or diazo-based polymerization initiators and peroxide-based polymerization initiators. Specifically, the method is the same as the method for forming the styrene-acrylic polymerization segment described above, so a description thereof will be omitted here.

[0164] From the viewpoint of achieving both low temperature fixability and hot offset resistance, the weight average molecular weight (Mw) of the amorphous vinyl resin is preferably within a range of 20000 to 150000, and the number average molecular weight (Mn) is preferably within a range of 5000 to 150000. The weight average molecular weight (Mw) and the number average molecular weight (Mn) can be measured in the same manner as in the case of the crystalline resin described above.

[0165] From the viewpoint of achieving both fixability and hot offset resistance, the glass transition temperature (Tg) of the amorphous vinyl resin is preferably within a range of 35 to 80° C. The glass transition temperature can be measured in the same manner as in the case of the amorphous resin described above.

[0166] (Hybrid amorphous polyester resin) The binder resin according to the present invention preferably contains a hybrid amorphous polyester resin, which has a suitable compatibility when used in combination with an amorphous vinyl resin, and which is advantageous in terms of shape controllability of the toner base particles and fixed image strength. By containing the hybrid amorphous polyester resin, it becomes easier to adjust compatibility / immiscibility and crystallization. The hybrid amorphous polyester resin can also be said to be a partially modified amorphous polyester resin.

[0167] The hybrid amorphous polyester resin preferably has a weight average molecular weight (Mw) in the range of 20,000 to 50,000. By being within the above range, it is easier to adjust the compatibility / imcompatibility and crystallization. The hybrid amorphous polyester resin preferably has a number average molecular weight (Mn) in the range of 3,000 to 12,500. The molecular weight can be measured in the same manner as in the case of the above-mentioned crystalline resin.

[0168] The hybrid amorphous polyester resin is a resin in which an amorphous polyester polymer segment and an amorphous polymer segment other than the amorphous polyester, preferably an amorphous vinyl polymer segment, are chemically bonded to each other.

[0169] The term "amorphous polyester polymerized segment" refers to a portion derived from an amorphous polyester resin. That is, it refers to a molecular chain having the same chemical structure as that constituting the amorphous polyester resin. The term "amorphous polymerized segment other than amorphous polyester" refers to a portion derived from an amorphous resin other than the amorphous polyester resin. Examples of the amorphous resin other than the amorphous polyester resin include vinyl resins such as styrene-acrylic resins, urethane resins, and urea resins. The amorphous polymerized segment other than the amorphous polyester may be used alone or in combination of two or more.

[0170] Therefore, a suitable amorphous vinyl polymer segment refers to a portion derived from an amorphous vinyl resin, that is, a molecular chain having the same chemical structure as that constituting an amorphous vinyl resin.

[0171] The hybrid amorphous polyester resin may be in any form, such as a block copolymer or a graft copolymer, so long as it contains an amorphous polyester polymer segment and an amorphous polymer segment other than the amorphous polyester, particularly an amorphous vinyl polymer segment, but is preferably a graft copolymer. By using the graft copolymer, low-temperature fixability, hot offset resistance, and mold release separability can be achieved at the same time.

[0172] From the above viewpoint, the amorphous polyester polymerized segment is preferably grafted to a main chain of an amorphous polymerized segment other than the amorphous polyester, particularly an amorphous vinyl polymerized segment. That is, the hybrid amorphous polyester resin is preferably a graft copolymer having a main chain of an amorphous polymerized segment other than the amorphous polyester, particularly an amorphous vinyl polymerized segment, and a side chain of an amorphous polyester polymerized segment.

[0173] The content of the hybrid amorphous polyester resin is preferably within a range of 3 to 20% by mass, and more preferably within a range of 5 to 15% by mass, based on the total mass of the binder resin.

[0174] (Amorphous polyester polymer segment) The amorphous polyester polymer segment is a portion derived from a known polyester resin obtained by a polycondensation reaction between a divalent or higher carboxylic acid (a polyvalent carboxylic acid component) and a divalent or higher alcohol (a polyhydric alcohol component), and refers to a polymer segment in which no clear endothermic peak is observed in DSC.

[0175] The amorphous polyester polymerized segment is not particularly limited as long as it is as defined above. For example, a resin having a structure in which other components are copolymerized in a main chain of an amorphous polyester polymerized segment, or a resin having a structure in which an amorphous polyester polymerized segment is copolymerized in a main chain of other components, corresponds to a hybrid amorphous polyester resin having an amorphous polyester polymerized segment in the present invention, so long as no clear endothermic peak is observed as described above.

[0176] (Polycarboxylic acid component) Examples of polyvalent carboxylic acid components include oxalic acid, succinic acid, maleic acid, adipic acid, β-methyladipic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, fumaric acid, citraconic acid, diglycolic acid, cyclohexane-3,5-diene-1,2-dicarboxylic acid, malic acid, citric acid, hexahydroterephthalic acid, malonic acid, pimelic acid, tartaric acid, mucic acid, phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-carbophthalic acid, and the like. Examples of the polycarboxylic acids include dicarboxylic acids such as xyphenylacetic acid, p-phenylene diacetic acid, m-phenylenediglycolic acid, p-phenylenediglycolic acid, o-phenylenediglycolic acid, diphenylacetic acid, diphenyl-p,p'-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, anthracene dicarboxylic acid, and dodecenyl succinic acid; trimellitic acid, pyromellitic acid, naphthalene tricarboxylic acid, naphthalene tetracarboxylic acid, pyrene tricarboxylic acid, and pyrene tetracarboxylic acid. These polycarboxylic acids may be used alone or in combination of two or more.

[0177] Among these, from the viewpoint of easily obtaining the effects of the present invention, it is preferable to use aliphatic unsaturated dicarboxylic acids such as fumaric acid, maleic acid, and mesaconic acid, aromatic dicarboxylic acids such as isophthalic acid and terephthalic acid, succinic acid, and trimellitic acid.

[0178] (Polyhydric alcohol component) Examples of the polyhydric alcohol component include dihydric alcohols such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, hexanediol, cyclohexanediol, octanediol, decanediol, dodecanediol, an ethylene oxide adduct of bisphenol A, and a propylene oxide adduct of bisphenol A; and trihydric or higher polyols such as glycerin, pentaerythritol, hexamethylolmelamine, hexaethylolmelamine, tetramethylolbenzoguanamine, and tetraethylolbenzoguanamine. These polyhydric alcohol components may be used alone or in combination of two or more.

[0179] Among these, dihydric alcohols such as an ethylene oxide adduct of bisphenol A and a propylene oxide adduct of bisphenol A are preferred from the viewpoint of easiness in achieving the effects of the present invention.

[0180] The use ratio of the polyvalent carboxylic acid component and the polyhydric alcohol component is preferably within the range of 1.5 / 1 to 1 / 1.5, more preferably within the range of 1.2 / 1 to 1 / 1.2, in terms of the equivalent ratio [-OH] / [-COOH] of the hydroxyl group [-OH] of the polyhydric alcohol component and the carboxyl group [-COOH] of the polyvalent carboxylic acid component. By using the polyvalent alcohol component and the polyvalent carboxylic acid component within the above range, it is easier to control the acid value and molecular weight of the amorphous polyester resin.

[0181] The method for forming the amorphous polyester polymer segment is not particularly limited, and the polymer segment can be formed by polycondensing (esterifying) the polyvalent carboxylic acid component and the polyhydric alcohol component using a known esterification catalyst.

[0182] The catalyst that can be used in producing the amorphous polyester polymer segment is the same as the catalyst explained in the above section (Crystalline resin), and therefore the explanation will be omitted here.

[0183] The polymerization temperature is not particularly limited, but is preferably within the range of 150 to 250° C. The polymerization time is not particularly limited, but is preferably within the range of 0.5 to 10 hours. During the polymerization, the reaction system may be decompressed as necessary.

[0184] The content of the amorphous polyester polymerized segment in the hybrid amorphous polyester resin is preferably within the range of 50 to 99.9% by mass, more preferably within the range of 70 to 95% by mass, based on the total mass of the hybrid amorphous polyester resin. By being within the above range, both heat resistance and low-temperature fixability can be achieved. The components and contents of each polymerized segment in the hybrid amorphous polyester resin can be determined, for example, by NMR measurement or methylation reaction Py-GC / MS measurement.

[0185] The hybrid amorphous polyester resin may further include a substituent such as a sulfonic acid group, a carboxy group, or a urethane group. The introduction of the substituent may be into the amorphous polyester polymer segment or into the amorphous vinyl polymer segment described below.

[0186] (Amorphous polymerized segment) In the present invention, the amorphous polymerization segment other than the amorphous polyester polymerization segment is also simply referred to as the “amorphous polymerization segment.” When an amorphous vinyl resin is contained in the binder resin, the amorphous polymerization segment (particularly the amorphous vinyl polymerization segment) can control the compatibility between the amorphous vinyl resin and the hybrid amorphous polyester resin.

[0187] The presence of an amorphous polymer segment in the hybrid amorphous polyester resin (and further in the toner) can be confirmed by identifying the chemical structure using, for example, NMR measurement or methylation reaction Py-GC / MS measurement.

[0188] In addition, when a resin having the same chemical structure and molecular weight as the amorphous polymerized segment is subjected to differential scanning calorimetry (DSC), the amorphous polymerized segment does not have a melting point and has a relatively high glass transition temperature (Tg). The glass transition temperature (Tg) of the resin having the same chemical structure and molecular weight as the amorphous polymerized segment is preferably within the range of 35 to 80°C, and more preferably within the range of 45 to 65°C.

[0189] In the hybrid amorphous polyester resin, it is preferable to replace a part of the amorphous polyester polymerized segment with an amorphous polymerized segment, and to have a structure in which the amorphous polyester polymerized segment and the amorphous polymerized segment are bonded.For example, a resin having a structure in which a polymer in which an amorphous polyester polymerized segment and an amorphous polymerized segment are bonded is copolymerized with other components in a main chain, or a resin having a structure in which a polymer in which an amorphous polyester polymerized segment and an amorphous polymerized segment are bonded is copolymerized with a main chain made of other components corresponds to the hybrid amorphous polyester resin having an amorphous polymerized segment in the present invention.

[0190] The amorphous polymerized segment is not particularly limited, and examples thereof include polymerized vinyl compounds, polymerized polyol components and isocyanate components, polymerized urea and formaldehyde, etc. Among them, amorphous vinyl polymerized segments obtained by polymerizing vinyl compounds are preferred, and examples thereof include acrylic acid ester polymerized segments, styrene-acrylic acid ester polymerized segments, ethylene-vinyl acetate polymerized segments, etc. These may be used alone or in combination of two or more.

[0191] Among the above vinyl polymerized segments, in consideration of the plasticity during thermal fixing, a styrene-acrylic ester polymerized segment (styrene-acrylic polymerized segment) is preferred. In addition, since the preferred form of the amorphous vinyl resin is a styrene-acrylic resin, the amorphous vinyl polymerized segment is also preferably a styrene-acrylic polymerized segment. By adopting such a form, the compatibility between the hybrid amorphous polyester resin and the amorphous vinyl resin is further improved, and the shape of the toner base particles can be easily controlled.

[0192] The monomers used to form the styrene-acrylic polymerized segment and the method of formation are the same as those described in the "styrene-acrylic polymerized segment" section of the hybrid crystalline polyester resin above, and therefore will not be described here.

[0193] The content of the amorphous polymerized segment in the hybrid amorphous polyester resin is preferably in the range of 0.1 to 50% by mass, more preferably in the range of 5 to 30% by mass, based on the total mass of the hybrid amorphous polyester resin. By being in the above range, the compatibility with the amorphous resin in the binder resin is improved, and low-temperature fixability, hot offset resistance, and heat resistance can be achieved at the same time.

[0194] The method for producing the hybrid amorphous polyester resin is not particularly limited as long as it is a method capable of forming a polymer in which the above-mentioned amorphous polyester polymerized segment and the amorphous polymerized segment are bonded together. Specific examples of the method for producing the hybrid amorphous polyester resin include the following methods.

[0195] (1) A method for producing a hybrid amorphous polyester resin, in which an amorphous polymer segment is polymerized in advance, and a polymerization reaction for forming an amorphous polyester polymer segment is carried out in the presence of the amorphous polymer segment.

[0196] (2) A method in which an amorphous polyester polymer segment and an amorphous polymer segment are formed in advance, and then these are bonded to produce a hybrid amorphous polyester resin.

[0197] (3) A method for producing a hybrid amorphous polyester resin by forming an amorphous polyester polymer segment in advance and then carrying out a polymerization reaction for forming an amorphous polymer segment in the presence of the amorphous polyester polymer segment.

[0198] Among the above formation methods (1) to (3), method (1) is preferred from the viewpoints of ease of formation of a hybrid amorphous polyester resin having a structure in which an amorphous polyester polymer segment is grafted to an amorphous polymer segment and of simplifying the production process.

[0199] Furthermore, the toner base particles may contain internal additives such as a colorant, a release agent, and a charge control agent, if necessary.

[0200] <1.1.3 Colorants> The magnetic material according to the present invention can function as a colorant, but can also be used in combination with conventionally used colorants. As the colorant, carbon black, dyes, pigments, etc. can be used arbitrarily, and as the carbon black, channel black, furnace black, acetylene black, thermal black, lamp black, etc. Also, a magnetic material can be used as the colorant.

[0201] Specific examples of white colorants include inorganic pigments (e.g., heavy calcium carbonate, light calcium carbonate, titanium oxide, aluminum hydroxide, titanium white, talc, calcium sulfate, barium sulfate, zinc oxide, magnesium oxide, magnesium carbonate, amorphous silica, colloidal silica, white carbon, kaolin, calcined kaolin, delaminated kaolin, aluminosilicate, sericite, bentonite, smexite, etc.), and organic pigments (e.g., polystyrene resin particles, urea-formaldehyde resin particles, etc.). In addition, pigments having a hollow structure, such as hollow resin particles and hollow silica, may also be mentioned. From the viewpoint of electrostatic chargeability and hiding power, the white colorant is preferably titanium oxide. Titanium oxide may have any crystal structure, such as anatase type, rutile type, or brookite type.

[0202] The white colorant has an average particle size preferably within a range of 10 to 1000 nm, and more preferably within a range of 50 to 500 nm. In addition, the white colorant may be subjected to a surface treatment to impart dispersibility.

[0203] Examples of black colorants that can be used include carbon blacks such as furnace black, channel black, acetylene black, thermal black, and lamp black, as well as magnetic powders such as magnetite and ferrite.

[0204] Examples of colorants for magenta or red include CI Pigment Red 2, CI Pigment Red 3, CI Pigment Red 5, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48;1, CI Pigment Red 53;1, CI Pigment Red 57;1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 150, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, Pigment Red 184, and CI Pigment Red 222.

[0205] Furthermore, examples of colorants for orange or yellow include CI Pigment Orange 31, CI Pigment Orange 43, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 15, CI Pigment Yellow 17, CI Pigment Yellow 74, CI Pigment Yellow 93, CI Pigment Yellow 94, CI Pigment Yellow 138, CI Pigment Yellow 155, CI Pigment Yellow 180, and CI Pigment Yellow 185.

[0206] Furthermore, examples of colorants for green or cyan include CI Pigment Blue 15, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 15:4, CI Pigment Blue 16, CI Pigment Blue 60, CI Pigment Blue 62, CI Pigment Blue 66, CI Pigment Green 7, and the like.

[0207] These may be used alone or in combination of two or more.

[0208] The average particle size of the colorant having a color other than white is preferably within a range of 10 to 1000 nm, and more preferably within a range of 50 to 500 nm.

[0209] The content of the colorant is preferably within a range of 1 to 60% by mass, and more preferably within a range of 2 to 25% by mass, based on the total mass of the toner base particles. By being within the above range, color reproducibility of the image can be ensured.

[0210] <1.1.4 Release agent> The toner of the present invention preferably contains a release agent (wax). Any known release agent can be used. Examples of the release agent include polyolefin waxes such as polyethylene wax and polypropylene wax, branched chain hydrocarbon waxes such as microcrystalline wax, long chain hydrocarbon waxes such as paraffin wax, Sasol wax, and Fischer-Tropsch wax, and dialkyl ketone waxes such as distearyl ketone, carnauba wax, montan wax, behenyl behenate (behenyl behenate), trimethylolpropane tribehenate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, tristearyl trimellitate, distearyl maleate, fatty acid polyglycerin ester, and amide waxes such as ethylenediamine behenylamide and tristearyl trimellitate amide.

[0211] The wax is easily compatible with the amorphous resin. Therefore, the plasticizing effect of the wax improves the sharp melting property of the toner particles, and the low-temperature fixability can be improved. From the viewpoint of further improving the low-temperature fixability, the wax is preferably an ester wax (ester compound), and from the viewpoint of achieving both heat resistance and low-temperature fixability, it is more preferably a linear ester wax (linear ester compound). These waxes may be used alone or in combination of two or more.

[0212] From the viewpoint of sufficient heat-resistant storage stability, low-temperature fixability and releasability, the melting point of the wax is preferably within the range of 40 to 160° C., more preferably within the range of 50 to 120° C., and even more preferably within the range of 70 to 80° C. By having the melting point of the wax within the above range, the heat-resistant storage stability of the toner is ensured, and even when fixing is performed at a low temperature, a stable toner image can be obtained without causing cold offset or the like. The melting point of the release agent can be measured in the same manner as the method for measuring the temperature (melting point) of the endothermic peak top described above.

[0213] The content of the release agent in the toner base particles is preferably within a range of 3 to 15% by mass relative to the total mass of the binder resin in the toner base particles. By being within the above range, both hot offset resistance and releasability can be achieved. If the content of the release agent is 3% by mass or more, sufficient releasability can be obtained, and if it is 15% by mass or less, sufficient heat resistance can be obtained.

[0214] <1.1.5 Charge control agents> The toner of the present invention preferably contains a charge control agent. The toner of the present invention is preferably a magnetic toner and a negatively chargeable toner. The charge control agent for negative charging is not particularly limited, but it is preferable to use an organic metal complex compound or a chelate compound, and examples thereof include a monoazo metal complex compound, an acetylacetone metal complex compound, a metal complex compound of an aromatic hydroxycarboxylic acid or an aromatic dicarboxylic acid, and the like.

[0215] Commercially available products may also be used, examples of which include Spilon (registered trademark) Black TRH, T-77, and T-95 (manufactured by Hodogaya Chemical Co., Ltd.), and BONTRON (registered trademark) S-34, S-44, S-54, E-84, E-88, and E-89 (manufactured by Orient Chemical Co., Ltd.). The charge control agent may be used alone or in combination of two or more kinds.

[0216] From the viewpoint of the charge amount, the content of the charge control agent is preferably within a range of 0.1 to 10% by mass, and more preferably within a range of 0.1 to 5% by mass, based on the total mass of the binder resin in the toner base particles.

[0217] <1.1.6 Structure and shape of toner base particles> (Structure of toner base particles) The structure of the toner base particles according to the present invention is not particularly limited, and may be a so-called single-layer structure or a core-shell structure. From the viewpoint of suppressing charge decay, low-temperature fixing property, hot offset resistance, and heat-resistant storage property, the core-shell structure is preferable.

[0218] An example of a core-shell structure is shown below. The core portion contains at least a binder resin and a magnetic material, and may further contain other additives (internal additives) such as a release agent, if necessary. The shell layer contains an amorphous resin.

[0219] Specifically, the core portion is preferably composed of a binder resin containing an amorphous vinyl resin and a crystalline polyester resin, and internal additives such as a magnetic material and a release agent, and the shell layer is preferably composed of a hybrid amorphous polyester resin.

[0220] The core-shell structure is not limited to a structure in which the shell layer completely covers the surface of the core particle, but also includes, for example, a structure in which the shell layer does not completely cover the surface of the core particle, and the surface of the core particle is exposed in places.

[0221] From the viewpoint of improving the chargeability under a high-temperature and high-humidity environment, it is preferable that the crystalline resin is not exposed on the surface but is contained inside the toner base particle, and the amorphous resin is exposed on the surface of the toner base particle. Such a form can be controlled by the timing of addition of each resin when producing the toner base particle by the emulsion aggregation method.

[0222] The morphology of the toner base particles, i.e., the cross-sectional structure of the core-shell structure and the location of the crystalline polyester resin, can be confirmed using known means such as a transmission electron microscope (TEM) or a scanning probe microscope (SPM).

[0223] (Toner base particle diameter) The particle size of the toner base particles is preferably in the range of 3 to 10 μm in terms of volume-based median diameter (D50). By being in the above range, the reproducibility of fine lines is high, high-quality images can be obtained, and toner fluidity can be ensured. Here, the volume-based median diameter (D50) of the toner base particles can be measured and calculated using, for example, a device in which a computer system for data processing is connected to a "Coulter Multisizer 3" (manufactured by Beckman Coulter, Inc.).

[0224] The volume-based median diameter of the toner base particles can be controlled by the concentration of the aggregating agent, the amount of solvent added, or the fusion time in the aggregation and fusion process during toner production described below, as well as the composition of the resin component.

[0225] (Average circularity of toner base particles) From the viewpoint of low-temperature fixability, the average circularity of the toner base particles is preferably within a range of 0.920 to 1.000, and more preferably within a range of 0.940 to 0.995.

[0226] The average circularity of the toner base particles is a value measured and calculated using, for example, "FPIA-2100" (manufactured by Sysmex Corporation). Specifically, the toner base particles are wetted with an aqueous surfactant solution, ultrasonically dispersed for one minute, and then measured using "FPIA-2100" under the measurement conditions of HPF (high magnification imaging) mode at an appropriate concentration with an HPF detection count of 4,000 particles. The circularity is calculated using the following formula.

[0227] Circularity = (perimeter of a circle with the same projected area as the particle image) / (perimeter of the projected particle image) The average circularity is an arithmetic mean value obtained by adding up the circularity of each particle and dividing the sum by the total number of particles measured.

[0228] In addition, the surface of the toner base particle has irregularities, and in the recesses, the magnetic material and the surface of the toner base particle are relatively close to each other. Therefore, it is necessary to cover the magnetic material with an external additive to prevent the magnetic material from being exposed on the surface of the toner particle. The strontium titanate particles according to the present invention can move freely while adhering to the surface of the toner base particle, and as a result, they tend to gather in the recesses, preventing the magnetic material from being exposed on the surface of the toner particle.

[0229] [1.2 External additives] The toner for developing electrostatic images of the present invention is characterized in that it contains, as an external additive, strontium titanate doped with a metal element other than titanium and strontium. The external additive is added from the viewpoint of improving the charging performance, fluidity, cleaning properties, etc. of the toner particles, and adheres to the surface of the toner base particles.

[0230] The external additive according to the present invention may be strontium titanate doped with a metal element other than titanium and strontium, or may be a conventionally known external additive.

[0231] Toner particles are capable of moving to a photosensitive drum or a recording medium by being charged, and therefore need to maintain the charge amount. However, since the toner of the present invention generally contains a magnetic material having low electrical resistance, the use of an external additive makes it possible to form a structure in which the magnetic material is not exposed on the surface of the toner particles, thereby suppressing charge decay.

[0232] Therefore, it is necessary to use an external additive having high electrical resistance, but since the toner particles need to move and adhere by electrostatic force, the surfaces of the toner particles containing the external additive need to be charged. In other words, it is preferable for the external additive to be one that has high resistance and is ferroelectric. Further, it is preferable that the toner particles interact with the magnetic material and suppress the magnetic material from being exposed on the surface of the toner particles.

[0233] The content of the external additive is preferably 0.1 to 10% by mass based on the total mass of the toner particles (toner base particles and external additive). As a device for attaching the external additives listed below to the toner base particles, various known mixing devices such as a Turbula mixer, a Henschel mixer, a Nauta mixer, and a V-type mixer can be used.

[0234] <1.2.1 Strontium titanate> Strontium titanate is a composite oxide of strontium and titanium, and has a perovskite structure. Such perovskite oxides are generally represented by the formula ABO3, and it is known that divalent elements such as Ca, Sr, Ba, and Pb occupy the A site, and tetravalent elements such as Ti, Zr, and Sn occupy the B site.

[0235] Strontium titanate has a perovskite structure, which gives it high crystallinity and high resistance. In fact, the ions that are regularly arranged are slightly misaligned, which causes polarization and makes it ferroelectric.

[0236] However, due to its high crystallinity, strontium titanate particles tend to assume a cubic or rectangular shape, making it difficult for them to adhere to toner base particles as an external additive. Therefore, by doping with a metal element other than titanium and strontium to change the crystal structure, the crystallinity is reduced and a rounded shape, i.e., particles with a small diameter and high circularity, can be obtained.

[0237] In addition, strontium titanate has a high crystallinity and therefore a high density compared to resins used as binder resins, and is therefore likely to be embedded in the toner base particles. However, this embedding is suppressed by interaction with the magnetic material.

[0238] By doping with a metal element and changing the crystal structure, the polarization state within the crystal also changes, but by adjusting the particle size, sufficient dielectric properties can be obtained as an external additive.

[0239] The metal element used is not particularly limited as long as it is other than titanium and strontium. It is preferable that the metal element has an ionic radius that can enter the crystal structure of strontium titanate when ionized. From this viewpoint, the metal element preferably has an ionic radius of 40 to 200 pm when ionized, more preferably 60 to 150 pm.

[0240] Examples of metal elements include lanthanoids, silicon, aluminum, calcium, magnesium, barium, phosphorus, sulfur, calcium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, yttrium, zinc, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, antimony, barium, tantalum, tungsten, rhenium, osmium, iridium, platinum, bismuth, yttrium, zirconium, niobium, silver, and tin. Lanthanoids are preferably lanthanum and cerium. Among these, lanthanum is preferred from the viewpoint of ease of doping and ease of control of the shape of strontium titanate particles.

[0241] From the viewpoint of controlling the volume resistivity and the electric capacitance, a metal element having an electronegativity of 2 or less, preferably 1.3 or less, and more preferably 1.2 or less, in terms of the Allred-Rochow value, is preferred. Suitable metal elements with an electronegativity of 2.0 or less are shown below along with their electronegativity. Metal elements with an electronegativity of 2.0 or less include lanthanum (1.08), magnesium (1.23), aluminum (1.47), silica (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), and cerium (1.06).

[0242] From the viewpoint of achieving a rounded shape while having a perovskite crystal structure, the amount of metal element in the strontium titanate particles is preferably within a range of 0.1 to 20 mol %, more preferably within a range of 0.1 to 15 mol %, and even more preferably within a range of 0.1 to 10 mol %, relative to strontium.

[0243] (Number average primary particle size of strontium titanate) In the present invention, the number average primary particle diameter of strontium titanate is the diameter of a circle having the same area as a primary particle image (so-called circle equivalent diameter), and the number average primary particle diameter of strontium titanate is the particle diameter that is 50% cumulative from the small diameter side in the number-based distribution of primary particles.

[0244] The number-average primary particle diameter of the strontium titanate according to the present invention is preferably within a range of 20 to 300 nm, more preferably within a range of 20 to 100 nm. By making it 20 nm or more, the effect as a charge control agent is sufficiently exhibited, and by making it 300 nm or less, the specific surface area becomes sufficiently large, and the hiding rate of the toner base particle surface by the external additive can be increased.

[0245] The number average primary particle diameter of strontium titanate is measured, for example, by the following method. After strontium titanate is externally added (dispersed) to the toner base particles, 100 primary particles of strontium titanate are observed at 40,000 times magnification using a scanning electron microscope "JSM-7401F" (manufactured by JEOL Ltd.), the longest and shortest diameters of each particle are measured by image analysis of the primary particles, and the midpoint between these diameters is used to measure the equivalent circle diameter. The average of the 100 measured primary particle diameters is then taken as the average primary particle diameter.

[0246] The number average primary particle size of strontium titanate can be controlled, for example, by adjusting various conditions when strontium titanate is produced by a wet process.

[0247] (Average circularity of strontium titanate) In the present invention, the average circularity of strontium titanate is the value obtained by dividing the perimeter of a circle having the same area as the primary particle image (so-called circle equivalent perimeter) by the perimeter of the primary particle image, and the average circularity of strontium titanate is the arithmetic mean value obtained by adding up the circularity of each primary particle and dividing it by the total number of particles measured. Note that a circularity of 1.0 means a perfect sphere, and the lower the value, the more uneven the surface is and the higher the degree of irregularity.

[0248] The strontium titanate according to the present invention preferably has an average circularity of primary particles in the range of 0.82 to 0.94. By making it 0.82 or more, the particles are less likely to be detached from the toner base particles, and by making it 0.94 or less, the movement on the surface of the toner base particles is restricted, and dispersibility is maintained.

[0249] The average circularity of the primary particles of strontium titanate is measured, for example, by the following method. 100 primary particles of strontium titanate are photographed at 40,000 times magnification using a scanning electron microscope "JSM-7401F" (manufactured by JEOL Ltd.), and this photographic image is scanned and subjected to image analysis using an image processing analyzer "LUZEX (registered trademark) AP" (manufactured by Nireco Corporation). From the analyzed image, the perimeter of a circle having the same projected area as the particle image and the perimeter of the particle projected image are obtained, and the circularity is calculated using the following formula. The circularity of each particle is then added together and divided by the total number of particles measured to calculate the average circularity.

[0250] Circularity = (perimeter of a circle with the same projected area as the particle image) / (perimeter of the projected particle image) = [2 × (Aπ) 1 / 2 ] / PM In the above formula, A represents the projected area of ​​strontium titanate, and PM represents the perimeter of strontium titanate.

[0251] (Hydrophobic surface) The strontium titanate according to the present invention has a hydrophobic surface, and thus can increase electrical resistance and prevent the charge of the toner from leaking.

[0252] From the viewpoint of increasing the resistance, the hydrophobic surface of strontium titanate is preferably surface-treated with a silicon-containing organic compound. Examples of the silicon-containing organic compound include alkoxysilane compounds, silazane compounds, silicone oils, etc., and among them, at least one selected from the group consisting of alkoxysilane compounds and silicone oils is preferable.

[0253] Examples of alkoxysilane compounds that are silicon-containing organic compounds include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, hexyltriethoxy ... Silane, decyltriethoxysilane, dodecyltriethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, phenyltriethoxysilane, benzyltriethoxysilane; dimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane; trimethylmethoxysilane, trimethylethoxysilane;

[0254] Examples of the silazane compound, which is a silicon-containing organic compound, include dimethyldisilazane, trimethyldisilazane, tetramethyldisilazane, pentamethyldisilazane, and hexamethyldisilazane.

[0255] Examples of silicone oils, which are silicon-containing organic compounds, include silicone oils such as dimethylpolysiloxane, diphenylpolysiloxane, and phenylmethylpolysiloxane; and reactive silicone oils such as amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, carbinol-modified polysiloxane, fluorine-modified polysiloxane, methacryl-modified polysiloxane, mercapto-modified polysiloxane, and phenol-modified polysiloxane.

[0256] Among these, from the viewpoint of improving the charging environment difference and the fluidity, it is preferable to use an alkoxysilane compound as the silicon-containing organic compound, and in particular, from the viewpoint of obtaining the charging environment difference, butyltrimethoxysilane is preferable.

[0257] In order to prevent fluctuations in the resistance value of the particle surface, the hydrophobized surface of the specific strontium titanate particles preferably has a mass ratio (Si / Sr) of silicon (Si) to strontium (Sr) calculated from qualitative and quantitative analysis by fluorescent X-ray analysis of 0.025 or more and 0.25 or less, and more preferably 0.05 or more and 0.20 or less.

[0258] Here, the fluorescent X-ray analysis of the hydrophobized surface of the specific strontium titanate particles is carried out by the following method. That is, qualitative and quantitative analysis measurements are performed using a fluorescent X-ray analyzer (Shimadzu Corporation, XRF1500) under conditions of X-ray output of 40 V, 70 mA, measurement area of ​​10 mmφ, and measurement time of 15 minutes. Here, the elements to be analyzed are oxygen (O), silicon (Si), titanium (Ti), strontium (Sr), and metal elements other than titanium and strontium (Me), and the mass ratio (%) of each element is calculated from the total of each measured element by referring to separately prepared calibration curve data that can quantify each element. The mass ratio (Si / Sr) is calculated based on the silicon (Si) mass ratio value and the strontium (Sr) mass ratio value obtained in this measurement.

[0259] (moisture content) The water content of the strontium titanate according to the present invention is preferably within a range of 1.5 to 10% by mass, and more preferably within a range of 2 to 5% by mass, from the viewpoint of easily narrowing the charge distribution of the toner and easily suppressing leakage of the charged charge of the toner.

[0260] The water content of strontium titanate can be measured as follows. 20 mg of the measurement sample is left to stand in a chamber at a temperature of 22°C and a relative humidity of 55% for 17 hours to adjust the humidity, and then heated from 30°C to 250°C at a temperature increase rate of 30°C / min in a nitrogen gas atmosphere in a room at a temperature of 22°C and a relative humidity of 55% using a thermobalance (Shimadzu TGA-50 model) to measure the heat loss (mass lost by heating). Then, the moisture content is calculated based on the measured heat loss using the following formula. Moisture content (mass%) = (heat loss from 30°C to 250°C) ÷ (mass after humidity adjustment before heating) × 100

[0261] The water content of strontium titanate can be controlled by producing strontium titanate by a wet process, various conditions during the wet process, the type of hydrophobizing agent, the amount of hydrophobizing treatment, and the like.

[0262] The content of strontium titanate is preferably within the range of 0.1 to 5 mass %, more preferably within the range of 0.5 to 3 mass %, and particularly preferably within the range of 0.7 to 2 mass %, relative to the total mass of the toner particles (toner base particles and external additives).

[0263] <1.2.2 Other external additives> The external additive according to the present invention may contain, in addition to strontium titanate, conventionally known inorganic particles, organic particles, lubricants, and the like.

[0264] Examples of inorganic particles include silica, sol-gel silica, titania, alumina, etc. These inorganic particles may be hydrophobized with a surface treatment agent such as a known silane coupling agent or silicone oil, if necessary. The size of the inorganic particles is preferably within the range of 2 to 50 nm, more preferably within the range of 7 to 30 nm, in terms of number average primary particle diameter.

[0265] As the organic particles, organic particles made of homopolymers such as styrene and methyl methacrylate, or copolymers thereof can be used. The size of the organic particles is preferably within a range of 10 to 2000 nm in terms of number average primary particle diameter, and the particle shape is preferably spherical.

[0266] The number average primary particle diameter of inorganic particles or organic particles can be calculated using an electron microscope photograph, for example, by image processing of an image taken with a transmission electron microscope, as in the case of strontium titanate. Alternatively, a 30,000x magnification photograph of a toner sample is taken with a scanning electron microscope, the photograph is scanned with a scanner, and the external additives present on the toner particle surface of the photograph are binarized using "LUZEX (registered trademark) AP" (manufactured by Nireco Corporation), the horizontal Feret diameters of 100 particles per type of external additive are calculated, and the average value is taken as the number average primary particle diameter.

[0267] Preferably, the volume average particle size measured with a laser diffraction / scattering particle size distribution analyzer, for example, "LA-750" (manufactured by Horiba, Ltd.) or the like is compared with the average particle size of inorganic particles or organic particles measured with an electron microscope to confirm that the numerical values ​​match, and further, by confirming that no aggregation of inorganic particles or organic particles occurs, the average particle size can be determined to be the particle size of primary particles. The number average primary particle size of the inorganic particles or organic particles can be adjusted, for example, by classification or mixing of classified particles.

[0268] Lubricants are used for the purpose of further improving cleaning properties and transferability. Examples include metal salts of higher fatty acids such as stearic acid salts of zinc, aluminum, copper, magnesium, calcium, etc., oleic acid salts of zinc, manganese, iron, copper, magnesium, etc., palmitic acid salts of zinc, copper, magnesium, calcium, etc., linoleic acid salts of zinc, calcium, etc., and ricinoleic acid salts of zinc, calcium, etc. The particle size of the lubricant is preferably within the range of 0.3 to 20 μm, more preferably within the range of 0.5 to 10 μm, in terms of volume average particle diameter. The volume average particle diameter of the lubricant can be measured in accordance with JIS Z8825-1-2013.

[0269] The content of external additives used in combination with strontium titanate is preferably 15 mass % or less, more preferably in the range of 3 to 10 mass %, and even more preferably in the range of 4 to 8 mass %, based on the total mass of the external additives including strontium titanate.

[0270] [1.3 Manufacturing method of toner for developing electrostatic images] (Method of manufacturing toner base particles) The method for producing the toner base particles is not particularly limited, and examples thereof include known methods such as a kneading and pulverizing method, a suspension polymerization method, an emulsion aggregation method, a dissolution suspension method, a polyester elongation method, and a dispersion polymerization method.

[0271] Among these, it is preferable to employ the emulsion aggregation method from the viewpoints of uniformity of particle size, controllability of shape, and ease of forming a core-shell structure. The emulsion aggregation method will be described below.

[0272] <Emulsification aggregation method> The emulsion aggregation method is a method in which a dispersion of resin particles (hereinafter also referred to as "resin particles") dispersed with a surfactant or dispersion stabilizer is mixed with a dispersion of toner particle components such as colorant particles, and an aggregating agent is added to aggregate the particles to the desired toner particle size, and thereafter, or simultaneously with the aggregation, the resin particles are fused together and the shape is controlled to form toner particles.

[0273] In the present invention, the magnetic toner is a magnetic material, and the magnetic material is mixed with a dispersion liquid of toner particle components, and the toner base particles are formed by aggregation and fusion. Since the magnetic material is black, a black magnetic toner can be obtained without adding a colorant. If necessary, a colorant may be added.

[0274] The resin particles may be composite particles formed of two or more layers made of resins having different compositions.

[0275] The resin particles can be produced, for example, by emulsion polymerization, mini-emulsion polymerization, phase inversion emulsification, etc., or by a combination of several production methods. When an internal additive is to be contained in the resin particles, it is preferable to use the mini-emulsion polymerization method.

[0276] When an internal additive is contained in the toner base particles, the internal additive may be contained in the resin particles. Alternatively, a dispersion liquid of internal additive particles containing only the internal additive may be separately prepared, and the internal additive particles may be aggregated together with the resin particles when the resin particles are aggregated.

[0277] Also, toner base particles having a core-shell structure can be obtained by the emulsion aggregation method. Specifically, first, binder resin particles for the core part and a magnetic material are aggregated (and fused) to prepare granular core parts, and then binder resin particles for the shell layer are added to the dispersion liquid of the core parts, and the binder resin particles for the shell layer are aggregated and fused to the surface of the core parts to form a shell layer that covers the surface of the core parts.

[0278] The binder resin according to the present invention preferably contains a crystalline resin and an amorphous resin. In the case of producing toner base particles by the emulsion aggregation method, as an embodiment, it is preferable to include a step (1) of preparing a crystalline resin particle dispersion liquid, an amorphous resin particle dispersion liquid, and a magnetic material dispersion liquid as a binder resin particle dispersion liquid (hereinafter also referred to as a preparation step), and a step (2) of mixing the crystalline resin particle dispersion liquid, the amorphous resin particle dispersion liquid, and the magnetic material dispersion liquid, and aggregating and fusing them (hereinafter also referred to as an aggregation and fusing step).

[0279] Each step will be described in detail below.

[0280] (1) Preparation process More specifically, step (1) includes the following crystalline resin particle dispersion preparation step, amorphous resin particle dispersion preparation step, and magnetic material dispersion preparation step, and further includes a release agent dispersion preparation step, a colorant dispersion preparation step, and the like, as required.

[0281] (1-1) Crystalline resin particle dispersion preparation step and amorphous resin particle dispersion preparation step The crystalline resin particle dispersion preparation process is a process of synthesizing a crystalline resin constituting the toner base particles and dispersing the crystalline resin in particulate form in an aqueous medium to prepare a dispersion of crystalline resin particles, whereas the amorphous resin particle dispersion preparation process is a process of synthesizing an amorphous resin constituting the toner base particles and dispersing the amorphous resin in particulate form in an aqueous medium to prepare a dispersion of amorphous resin particles.

[0282] A method for dispersing a crystalline resin in an aqueous medium includes dissolving or dispersing the crystalline resin in an organic solvent (solvent) to prepare an oil phase liquid, dispersing the oil phase liquid in an aqueous medium by phase inversion emulsification or the like to form oil droplets controlled to a desired particle size, and then removing the organic solvent. The same applies to a method for dispersing an amorphous resin in an aqueous medium.

[0283] The organic solvent (solvent) used in the preparation of the oil phase liquid is preferably one having a low boiling point and low solubility in water, from the viewpoint of easy removal treatment after the formation of oil droplets, and examples thereof include methyl acetate, ethyl acetate, methyl ethyl ketone, isopropyl alcohol, methyl isobutyl ketone, toluene, xylene, etc. These may be used alone or in combination of two or more.

[0284] The amount of organic solvent (solvent) used (the total amount used when two or more types are used) is preferably within the range of 1 to 300 mass %, more preferably within the range of 10 to 200 mass %, and even more preferably within the range of 25 to 100 mass %, based on the total mass of the resin.

[0285] From the viewpoint of stable and smooth emulsification, it is necessary to make the carboxyl group in the oil phase have a proton (H + In order to promote the dissociation, it is preferable to add ammonia, sodium hydroxide, or the like to the oil phase liquid.

[0286] The amount of the aqueous medium used is preferably within a range of 50 to 2,000% by mass, more preferably within a range of 100 to 1,000% by mass, based on the total mass of the oil phase liquid. By using an amount of the aqueous medium within the above range, the oil phase liquid can be emulsified and dispersed to a desired particle size in the aqueous medium.

[0287] A dispersion stabilizer may be dissolved in the aqueous medium, and a surfactant, resin particles, etc. may be added thereto for the purpose of improving the dispersion stability of the oil droplets.

[0288] Examples of the dispersion stabilizer include inorganic compounds such as tricalcium phosphate, calcium carbonate, titanium oxide, colloidal silica, hydroxyapatite, etc. From the viewpoint of removing the dispersion stabilizer from the obtained toner base particles, it is preferable to use one that is soluble in acid or alkali, such as tricalcium phosphate, and from the viewpoint of the environment, it is preferable to use one that is decomposable by enzymes.

[0289] Examples of the surfactant include anionic surfactants such as alkylbenzene sulfonate, α-olefin sulfonate, phosphate ester, sodium alkyldiphenyl ether disulfonate, and sodium polyoxyethylene lauryl ether sulfate; amine salt type surfactants such as alkylamine salts, aminoalcohol fatty acid derivatives, polyamine fatty acid derivatives, and imidazolines; cationic surfactants of quaternary ammonium salt type such as alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkyldimethylbenzylammonium salts, pyridinium salts, alkylisoquinolinium salts, and benzethonium chloride; nonionic surfactants such as fatty acid amide derivatives and polyhydric alcohol derivatives; amphoteric surfactants such as alanine, dodecyldi(aminoethyl)glycine, di(octylaminoethyl)glycine, and N-alkyl-N,N-dimethylammonium betaine; and anionic surfactants and cationic surfactants having a fluoroalkyl group can also be used.

[0290] From the viewpoint of dispersion stability, the resin particles preferably have a particle diameter within the range of 0.5 to 3 μm. Specific examples include polymethyl methacrylate resin particles having particle diameters of 1 μm and 3 μm, polystyrene resin particles having particle diameters of 0.5 μm and 2 μm, and polystyrene-acrylonitrile resin particles having a particle diameter of 1 μm.

[0291] Such emulsification and dispersion of the oil phase liquid can be carried out by utilizing mechanical energy, and the dispersing machine for carrying out the emulsification and dispersion is not particularly limited, and examples thereof include a low-speed shear type dispersing machine, a high-speed shear type dispersing machine, a friction type dispersing machine, a high-pressure jet type dispersing machine, an ultrasonic dispersing machine such as an ultrasonic homogenizer, and a high-pressure impact type dispersing machine, an ultimaizer, and the like.

[0292] The organic solvent can be removed after the formation of the oil droplets by gradually increasing the temperature of the entire dispersion in which the crystalline resin particles are dispersed in the aqueous medium while stirring, and then strongly stirring the dispersion at a certain temperature range, followed by desolvation. Alternatively, the organic solvent can be removed while reducing the pressure using an evaporator or other device. The organic solvent can also be removed from the amorphous resin microparticles after the formation of the oil droplets in the same manner as the crystalline resin particles described above.

[0293] The average particle size of the crystalline resin particles (oil droplets) or amorphous resin particles (oil droplets) in the crystalline resin particle dispersion or amorphous resin particle dispersion thus obtained is preferably within the range of 60 to 1000 nm, more preferably within the range of 80 to 500 nm. The average particle size of the resin particles, magnetic particles, release agent, etc. can be measured with a laser diffraction / scattering type particle size distribution measuring device (Microtrack particle size distribution measuring device "UPA-150" (manufactured by Nikkiso Co., Ltd.)). The average particle size of these resin particles (oil droplets) can be controlled by the magnitude of the mechanical energy during emulsification and dispersion.

[0294] The content of the crystalline resin particles or the amorphous resin particles in the crystalline resin particle dispersion or the amorphous resin particle dispersion is preferably within a range of 10 to 50% by mass, more preferably within a range of 15 to 40% by mass, based on the total mass of the dispersion. By being within the above range, the broadening of the particle size distribution can be suppressed, and the toner properties can be improved.

[0295] (1-2) Magnetic dispersion preparation process The magnetic material dispersion preparation step is a step of dispersing a magnetic material in a particulate form in an aqueous medium to prepare a dispersion of magnetic particles.

[0296] The aqueous medium is as described in (1-1) above, and the surfactant, resin particles, and the like described in (1-1) above may be added to this aqueous medium for the purpose of improving the dispersion stability.

[0297] The magnetic material can be dispersed by utilizing mechanical energy. Such a dispersing machine is not particularly limited, and examples thereof include, as mentioned above, a low-speed shear type dispersing machine, a high-speed shear type dispersing machine, a friction type dispersing machine, a high-pressure jet type dispersing machine, an ultrasonic dispersing machine such as an ultrasonic homogenizer, or a high-pressure impact type dispersing machine such as an ultimaizer.

[0298] The content of the magnetic material in the magnetic material dispersion liquid is preferably within a range of 35 to 50% by mass, more preferably within a range of 40 to 50% by mass, based on the total mass of the dispersion liquid. By being within the above range, the magnetic attraction force with the magnet roll in the developing sleeve becomes appropriate.

[0299] (1-3) Release agent particle dispersion preparation process This release agent particle dispersion preparation process is a process that is carried out as necessary when it is desired to contain a release agent in the toner base particles, and is a process in which the release agent is dispersed in particulate form in an aqueous medium to prepare a dispersion of release agent particles.

[0300] The aqueous medium is as described in (1-1) above, and from the viewpoint of dispersion stability, the aqueous medium may contain the surfactants and resin particles described in (1-1) above.

[0301] The release agent can be dispersed by utilizing mechanical energy, and the dispersing machine is not particularly limited, and examples thereof include, as mentioned above, a low-speed shear dispersing machine, a high-speed shear dispersing machine, a friction dispersing machine, a high-pressure jet dispersing machine, an ultrasonic dispersing machine such as an ultrasonic homogenizer, a high-pressure impact dispersing machine, an ultimaizer, a high-pressure homogenizer, etc. When dispersing the release agent particles, heating may be performed as necessary.

[0302] The content of the release agent particles in the release agent particle dispersion liquid is preferably within a range of 10 to 50% by mass, more preferably within a range of 15 to 40% by mass, based on the total mass of the dispersion liquid. By being within the above range, the effect of ensuring hot offset resistance and separability can be obtained.

[0303] (1-4) Colorant dispersion preparation process The colorant dispersion preparation step is a step of dispersing a colorant in a particulate form in an aqueous medium to prepare a dispersion of colorant particles.

[0304] The aqueous medium is as described in (1-1) above, and from the viewpoint of dispersion stability, the aqueous medium may contain the surfactants and resin particles described in (1-1) above.

[0305] The colorant can be dispersed by utilizing mechanical energy. Such a dispersing machine is not particularly limited, but as mentioned above, examples include a low-speed shear type dispersing machine, a high-speed shear type dispersing machine, a friction type dispersing machine, a high-pressure jet type dispersing machine, an ultrasonic dispersing machine such as an ultrasonic homogenizer, or a high-pressure impact type dispersing machine such as an ultimizer.

[0306] The content of the colorant in the colorant dispersion is preferably within a range of 10 to 50% by mass, and more preferably within a range of 15 to 40% by mass, for each color, based on the total mass of the dispersion. By keeping the content within the above range, there is an effect of ensuring color reproducibility.

[0307] (2) Agglomeration / fusion process Crystalline resin particle dispersion, amorphous resin particle dispersion, magnetic material dispersion, and, if necessary, other components such as release agent particle dispersion and colorant dispersion are added and mixed. Next, the particles are slowly aggregated while balancing the repulsive force of the particle surface due to pH adjustment and the aggregation force due to the aggregating agent made of an electrolyte. Then, association is performed while controlling the average particle size and particle size distribution, and at the same time, the particles are fused together by heating and stirring to control the shape, forming toner particles. This aggregation and fusion process can also be performed using mechanical energy or heating means if necessary.

[0308] In the aggregation step, first, the obtained dispersions are mixed to form a mixed liquid, which is then heated at a temperature equal to or lower than the glass transition temperature of the amorphous resin to aggregate and form aggregated particles. The aggregated particles are formed by making the pH of the mixed liquid acidic under stirring. The pH is preferably within the range of 2 to 7, more preferably within the range of 2 to 6, and even more preferably within the range of 2 to 5.

[0309] In the aggregation step, it is preferable to use an aggregating agent. The aggregating agent is not particularly limited, but a surfactant having a polarity opposite to that of the surfactant used in the dispersant, an inorganic metal salt, or a complex containing a divalent or higher metal can be suitably used.

[0310] Examples of inorganic metal salts include metal salts such as sodium chloride, potassium chloride, lithium chloride, calcium chloride, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, copper sulfate, magnesium sulfate, aluminum sulfate, manganese sulfate, and calcium nitrate, as well as inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, polyiron silica, and calcium polysulfide. Among these, aluminum salts and polyaluminum chloride are particularly preferred. In order to obtain a sharper particle size distribution, the valence of the inorganic metal salt is more preferably divalent than monovalent, more preferably trivalent than divalent, and more preferably tetravalent than trivalent.

[0311] The content of divalent or higher metal ions in the toner base particles can be controlled mainly by adjusting the pH of the mixed liquid in this step, the content and type of the coagulant, and the like.

[0312] When the aggregated particles reach the desired particle size, crystalline resin particles and / or amorphous resin particles can be added to produce a toner having a configuration in which the surfaces of the core aggregated particles are coated with crystalline resin and / or amorphous resin (particles having a core-shell structure). When adding, an aggregating agent may be added or the pH may be adjusted before the addition.

[0313] During aggregation, it is preferable to heat and increase the temperature. In this case, if the temperature reaches the fusion temperature or higher by heating and increasing the temperature, the fusion process will also proceed at the same time. The temperature increase rate is preferably within the range of 0.1 to 5°C / min. In addition, the heating temperature (peak temperature) is preferably within the range of 40 to 100°C.

[0314] The average particle size of the aggregated particles is not particularly limited, but is preferably within the range of 4.5 to 7 μm. When the aggregated particles reach a desired particle size, an aggregation terminator is added to suppress and stop the aggregation of various particles in the reaction system (hereinafter, also referred to as the aggregation termination step), thereby controlling the particle size. The aggregation terminator refers to a basic compound that can adjust the pH in a direction away from a pH environment in which the aggregation action is promoted. In the aggregation termination step, the pH of the reaction system is preferably adjusted to 5 to 9.

[0315] Examples of the flocculation stopper (basic compound) include alkali metal salts such as ethylenediaminetetraacetic acid (EDTA) and its sodium salt, gluconal, sodium gluconate, potassium citrate and sodium citrate, nitrotriacetate (NTA) salt, GLDA (commercially available L-glutamic acid-N,N-diacetic acid), humic acid and fulvic acid, maltol and ethyl maltol, pentaacetic acid and tetraacetic acid, known compounds having both functional groups of carboxyl groups and hydroxyl groups such as tetrasodium 3-hydroxy-2,2'-iminodisuccinate, or their salts or water-soluble polymers (polymer electrolytes), sodium hydroxide, potassium hydroxide, etc. In the flocculation stop step, stirring may be performed in accordance with the flocculation step.

[0316] The fusion step is a step in which, after the above-mentioned aggregation stopping step or simultaneously with the aggregation step, the reaction system is heated to a desired fusion temperature to fuse the individual particles that constitute the aggregated particles together, thereby fusing the aggregated particles to form fused particles.

[0317] The fusion temperature in the fusion step is preferably equal to or higher than the melting point of the crystalline resin, and is preferably 0 to 20° C. higher than the melting point of the crystalline resin. The heating time may be long enough to effect fusion, and may be about 0.5 to 10 hours.

[0318] In the aggregation / fusion step, in order to stably disperse each particle in the system, a surfactant having the same meaning as the surfactant used in the above (1-1) crystalline resin particle dispersion preparation step / amorphous resin particle dispersion preparation step, etc. may be added to the aqueous medium.

[0319] The addition ratio (mass ratio) of the amorphous resin particles / crystalline resin particles in the aggregation and fusion step is preferably from 1 to 100. When the ratio is within the above range, the toner has excellent hot offset resistance and low-temperature fixing ability.

[0320] In addition, when other internal additives are introduced into the toner base particles, a method is preferable in which an internal additive particle dispersion liquid containing only the internal additives is prepared, and in the aggregation and fusion step, the internal additive particle dispersion liquid is mixed with a crystalline resin particle dispersion liquid, an amorphous resin particle dispersion liquid, and a magnetic material dispersion liquid.

[0321] After fusion, the mixture is cooled to obtain fused particles. The cooling rate is preferably 1 to 20° C. / min.

[0322] When the toner is obtained by the emulsion aggregation method, it is preferable to have a circularity control step (3) for controlling the circularity of the toner after the aggregation and fusion step.

[0323] (3) Circularity control process Specifically, the circularity control treatment may be a heat treatment in which the particles obtained in the aggregation and fusion process are heated. The circularity can be controlled by adjusting the heating temperature and holding time. By increasing the heating temperature or lengthening the holding time, the circularity can be brought closer to 1.

[0324] The heating temperature in the circularity control treatment is preferably within a range of 70 to 95° C. The circularity of particles having a particle diameter of 2 μm or more is measured using a circularity measuring device during heating, and it is possible to control the circularity by appropriately determining whether or not the circularity is as desired.

[0325] (4) Filtration and washing process The obtained dispersion of the toner base particles is cooled, and the toner base particles are separated from the dispersion using a solvent such as water, followed by a filtration process to filter out the toner base particles, and a washing process to remove any attached substances such as surfactants from the filtered toner base particles (cake-like aggregates).

[0326] The specific method of solid-liquid separation and washing is not particularly limited, and examples thereof include centrifugation, reduced pressure filtration using an aspirator, a Nutsche, etc., and filtration using a filter press, etc. In the filtration and washing steps, pH adjustment, pulverization, etc. may be carried out once or repeatedly as appropriate.

[0327] (5) Drying process The washed toner base particles are dried. The dryer used in the drying step is not particularly limited, but examples include ovens, spray dryers, vacuum freeze dryers, reduced pressure dryers, stationary shelf dryers, moving shelf dryers, fluidized bed dryers, rotary dryers, and stirring dryers. The moisture content of the dried toner base particles, as measured by Karl Fischer coulometric titration, is preferably 5% by mass or less, and more preferably 2% by mass or less.

[0328] In addition, when the dried toner base particles are aggregated by weak interparticle attractive forces to form aggregates, the aggregates may be disintegrated. The disintegration device is not particularly limited, and examples thereof include mechanical disintegration devices such as a jet mill, a Comil, a Henschel mixer, a coffee mill, and a food processor.

[0329] (Method of manufacturing strontium titanate) The method for producing the strontium titanate particles according to the present invention is not particularly limited, but from the viewpoint of controlling the particle size and shape, a wet production method is preferable. For example, there can be mentioned a production method in which an alkaline aqueous solution is added to a mixed liquid of a titanium oxide source and a strontium source to cause a reaction, and then an acid treatment is performed.

[0330] In the above production method, a dopant source is added to a mixed solution of a titanium oxide source and a strontium source, or a dopant source is added simultaneously with the addition of an alkaline aqueous solution, thereby obtaining strontium titanate doped with a metal element other than titanium and strontium.

[0331] Furthermore, the particle size of the strontium titanate particles can be controlled by the mixing ratio of the titanium oxide source and the strontium source, the concentration of the titanium oxide source at the start of the reaction, and the temperature and rate at which the aqueous alkaline solution is added.

[0332] The titanium oxide source is preferably a mineral acid peptized product of a hydrolyzate of a titanium compound. Specifically, metatitanic acid obtained by a sulfuric acid method and having an SO3 content of 1.0 mass % or less, preferably 0.5 mass % or less, is peptized with hydrochloric acid to adjust the pH to within a range of 0.8 to 1.5, from the viewpoint of obtaining strontium titanate particles with a good particle size distribution.

[0333] The strontium source may, for example, be strontium nitrate or strontium chloride.

[0334] The mixing ratio of the titanium oxide source and the strontium source is preferably within a range of 0.9 to 1.4, and more preferably within a range of 1.05 to 1.20, in terms of the SrO / TiO2 molar ratio. The concentration of the titanium oxide source at the start of the reaction is preferably within a range of 0.05 to 1.3 mol / L, and more preferably within a range of 0.5 to 1.0 mol / L, in terms of TiO2.

[0335] The dopant source is preferably an oxide of a metal element other than titanium and strontium. The metal oxide as the dopant source is preferably added as a solution in, for example, nitric acid, hydrochloric acid, or sulfuric acid.

[0336] As described above, the doping metal element is preferably lanthanum, and examples of the lanthanum-containing dopant source include lanthanum nitrate hexahydrate and lanthanum chloride heptahydrate.

[0337] Examples of the alkaline aqueous solution include an aqueous sodium hydroxide solution. The higher the temperature at which the alkaline aqueous solution is added, the better the crystallinity, so it is preferably within the range of 50 to 101°C. The slower the rate at which the alkaline aqueous solution is added, the larger the particle size becomes, and the faster the rate at which the aqueous solution is added, the smaller the particle size becomes, so it is preferably within the range of 0.001 to 1.2 equivalents / h, and more preferably within the range of 0.002 to 1.1 equivalents / h, relative to the raw material. The rate of addition may be changed midway depending on the purpose.

[0338] In the above reaction process, in order to prevent the production of strontium carbonate, it is preferable to prevent contamination with carbon dioxide gas by, for example, carrying out the reaction under a nitrogen gas atmosphere.

[0339] After the addition of the alkaline aqueous solution, the unreacted strontium source can be removed by performing an acid treatment. For example, the pH of the reaction solution is adjusted to within a range of 2.5 to 7.0, more preferably within a range of 4.5 to 6.0, using hydrochloric acid. After the acid treatment, the reaction liquid is subjected to solid-liquid separation, and the solid content is dried to obtain strontium titanate particles.

[0340] The obtained strontium titanate can be surface-treated as necessary. The method of surface treatment is not particularly limited. For example, in the case of hydrophobization, a treatment liquid is prepared by mixing the above-mentioned hydrophobization agent and a solvent, and the strontium titanate particles and the treatment liquid are mixed under stirring, and further stirring is continued. After the surface treatment, a drying process is performed in order to remove the solvent from the treatment liquid. As described above, the hydrophobization agent is preferably a silicon-containing organic material, and one type may be used alone, or two or more types may be used in combination.

[0341] As the solvent used in preparing the treatment liquid, when the hydrophobic treatment agent is an alkoxysilane compound or a silazane compound, alcohols (e.g., methanol, ethanol, propanol, butanol) are preferred, and when the hydrophobic treatment agent is a silicone oil, hydrocarbons (e.g., benzene, toluene, normal hexane, normal heptane) are preferred.

[0342] In the treatment liquid, the concentration of the hydrophobizing agent is preferably within the range of 1 to 50% by mass, more preferably within the range of 5 to 40% by mass, and further preferably within the range of 10 to 30% by mass.

[0343] The amount of the hydrophobizing agent used in the surface treatment may be determined depending on the target volume resistivity, etc., and is, for example, preferably in the range of 1 to 50 parts by mass, more preferably in the range of 5 to 40 parts by mass, and even more preferably in the range of 5 to 30 parts by mass, per 100 parts by mass of strontium titanate particles.

[0344] The moisture content of the strontium titanate particles can be controlled by adjusting the conditions of the drying treatment after the surface treatment. For example, the drying conditions are preferably such that the drying temperature is within the range of 90 to 300°C (more preferably, within the range of 100 to 150°C) and the drying time is within the range of 1 to 15 hours (more preferably, within the range of 5 to 10 hours).

[0345] Alternatively, the hydrophobic treatment may be carried out by spraying the hydrophobic treatment agent onto the strontium titanate particles or by mixing the vaporized hydrophobic treatment agent onto the particles and then carrying out the heat treatment. In this case, water, amines, or other catalysts may be used, and the treatment is preferably carried out under an inert gas atmosphere such as nitrogen.

[0346] (External additive addition process) The toner of the present invention is obtained by adding an external additive containing strontium titanate to the toner base particles obtained by the above-mentioned production method and adhering the external additive to the surface of the toner base particles. If necessary, the toner may contain an external additive other than strontium titanate. The device for mixing the dried toner base particles with the external additive is not particularly limited, and examples thereof include various known mixing devices such as a Turbula mixer, a Henschel mixer, a Nauta mixer, a V-type mixer, a sample mill, etc. In order to set the particle size distribution of the toner in an appropriate range, sieve classification may be performed as necessary.

[0347] ≪2 Image forming method≫ The image forming method of the present invention is characterized by using the toner for developing electrostatic images of the present invention. The toner of the present invention is a magnetic toner and can be used as a one-component developer. Such a one-component developer can be suitably used in a one-component contact development system.

[0348] The one-component contact development method is a development method in which a toner carrier and an electrostatic image carrier are arranged in contact (contact arrangement), and these carriers transport the toner by rotating. Since a large shear is applied to the contact portion between the toner carrier and the electrostatic image carrier, in order to obtain a high-quality image, it is preferable that the toner has high durability and high fluidity. The toner of the present invention is a toner with excellent durability and can be suitably used in the one-component contact development method.

[0349] Compared to the two-component development method that uses a carrier, the one-component development method requires less developer because it does not have a carrier, making it possible to make the cartridge that contains the developer smaller. Also, the contact development method reduces toner scattering and can obtain high-quality images. In other words, the one-component contact development method, which combines both of these, can achieve both a smaller development device and high image quality.

[0350] ≪3 Image forming device≫ The image forming apparatus of the present invention is an image forming apparatus comprising an electrostatic image holding means, a charging means, an electrostatic image forming means, a developing means, a transferring means and a fixing means, and is characterized in that it uses the toner for developing electrostatic images of the present invention.

[0351] Specifically, the image forming apparatus used in the present invention includes electrostatic image holding means for holding an electrostatic image, charging means for charging the surface of the electrostatic image holding member, electrostatic image forming means for forming an electrostatic image on the surface of the charged electrostatic image holding member, developing means for containing an electrostatic image developer and developing the electrostatic image formed on the surface of the electrostatic image holding member as a toner image with the electrostatic image developer, transfer means for transferring the toner image formed on the surface of the electrostatic image holding member to the surface of a recording medium, and fixing means for fixing the toner image transferred to the surface of the recording medium. The electrostatic image developer used is the toner for developing electrostatic images of the present invention.

[0352] The image forming apparatus implements an image forming method including an electrostatic image retaining step of retaining an electrostatic image, a charging step of charging the surface of an electrostatic image retainer, an electrostatic image forming step of forming an electrostatic image on the charged surface of the electrostatic image retainer, a developing step of containing an electrostatic image developer and developing the electrostatic image formed on the surface of the electrostatic image retainer as a toner image using the electrostatic image developer, a transfer step of transferring the toner image formed on the surface of the electrostatic image retainer to the surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium.

[0353] The image forming apparatus of the present invention may be a known image forming apparatus such as a direct transfer type apparatus in which a toner image formed on the surface of an electrostatic image holder is directly transferred to a recording medium; an intermediate transfer type apparatus in which a toner image formed on the surface of an electrostatic image holder is primarily transferred to the surface of an intermediate transfer body, and the toner image transferred to the surface of the intermediate transfer body is secondarily transferred to the surface of a recording medium; an apparatus provided with a cleaning means for cleaning the surface of the electrostatic image holder after the transfer of the toner image and before charging; or an apparatus provided with a discharging means for irradiating the surface of the image holder with discharging light to discharge it after the transfer of the toner image and before charging.

[0354] Furthermore, when the image forming apparatus of the present invention is an apparatus of the intermediate transfer type, the transfer means may be configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means which primarily transfers the toner image formed on the surface of the electrostatic image holder onto the surface of the intermediate transfer body, and a secondary transfer means which secondarily transfers the toner image transferred onto the surface of the intermediate transfer body onto the surface of a recording medium.

[0355] In the image forming apparatus of the present invention, for example, a portion including the developing means may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge equipped with a developing means containing the toner for developing electrostatic images of the present invention is preferably used.

[0356] A one-component contact development method that can be suitably used in the image forming apparatus of the present invention will now be described in detail with reference to the drawings.

[0357] Fig. 1 is a schematic cross-sectional view showing an example of a developing device, and Fig. 2 is a schematic cross-sectional view showing an example of an image forming apparatus using a one-component contact development system. 1 or 2, the electrostatic image carrier 45 on which the electrostatic image is formed is rotated in the direction of arrow R1. The toner carrier 47 rotates in the direction of arrow R2 to transport toner 57 to a development area where the toner carrier 47 and the electrostatic image carrier 45 face each other. A toner supplying member 48 is in contact with the toner carrier 47, and supplies toner 57 to the surface of the toner carrier 47 by rotating in the direction of arrow R3. The toner 57 is stirred by a stirring member 58.

[0358] Around the electrostatic image carrier 45, there are provided a charging member (charging roller) 46, a transfer member (transfer roller) 50, a cleaner container 43, a cleaning blade 44, a fixing device 51, a pickup roller 52, etc. The electrostatic image carrier 45 is charged by the charging roller 46. Then, exposure is performed by irradiating the electrostatic image carrier 45 with laser light by a laser generating device 54, and electrostatic charges corresponding to the target image are formed.

[0359] The electrostatic image on the electrostatic image carrier 45 is developed with toner 57 in a developing device 49 to obtain a toner image. The toner image is transferred onto a transfer material (paper) 53 by a transfer member (transfer roller) 50 that is in contact with the electrostatic image carrier 45 via the transfer material. The toner image may be transferred onto the transfer material via an intermediate transfer body. The transfer material (paper) 53 carrying the toner image is transported to a fixing device 51, where it is fixed onto the transfer material (paper) 53. In addition, the toner 57 that remains partly on the electrostatic image carrier 45 is scraped off by a cleaning blade 44 and stored in a cleaner container 43. It is also preferable that a toner regulating member (reference numeral 55 in FIG. 1) contacts the toner carrier via the toner to regulate the toner layer thickness on the toner carrier. In this way, high image quality without regulation failure can be obtained. A regulating blade is generally used as the toner regulating member that contacts the toner carrier.

[0360] The base portion, which is the upper side of the regulating blade, is fixed to the developing device side, and the lower side is bent in the forward or reverse direction of the toner carrier against the elastic force of the blade and abutted against the surface of the toner carrier with an appropriate elastic pressing force. For example, the toner regulating member 55 may be fixed to the developing device by sandwiching one free end of the toner regulating member 55 between two fixing members (e.g., a metal elastic body, reference numeral 56 in FIG. 1) as shown in FIG. 1 and fixing it with screws. EXAMPLES

[0361] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the examples, the terms "parts" and "%" are used, but they represent "parts by mass" or "% by mass" unless otherwise specified.

[0362] Example 1 Toner particles 1 to 13 were prepared according to the procedure described below, and each toner was evaluated.

[0363] [Preparation of toner base particles 1 to 4] <Preparation of toner base particles 1> (Synthesis of amorphous polyester A1) Terephthalic acid 48.0 parts by mass Dodecenyl succinic acid 17.0 parts by mass Trimellitic acid 10.2 parts by mass Bisphenol A ethylene oxide (2 moles) adduct 80.0 parts by mass Bisphenol A propylene oxide (2 moles) adduct 74.0 parts by mass Dibutyltin oxide 0.1 parts by mass

[0364] The above materials were placed in a heated and dried two-neck flask, and nitrogen gas was introduced into the vessel to maintain an inert atmosphere and the temperature was raised while stirring. After that, a condensation polymerization reaction was carried out at 150°C to 230°C for about 13 hours, and then the pressure was gradually reduced at 210°C to 250°C to obtain amorphous polyester A1.

[0365] The amorphous polyester A1 had a number average molecular weight (Mn) of 21,200, a weight average molecular weight (Mw) of 98,000, and a glass transition temperature (Tg) of 58.3°C.

[0366] (Preparation of resin solution) Ethyl acetate 100.0 parts by mass Amorphous polyester A1 30.0 parts by mass Sodium hydroxide (0.1 mol / L) 0.3 parts by mass Anionic surfactant (Daiichi Kogyo Seiyaku Co., Ltd., Neogen RK) 0.2 parts by mass

[0367] The above materials were placed in a beaker equipped with a stirrer, heated to 60.0° C., and stirred until completely dissolved, to obtain a resin solution A1.

[0368] (Preparation of amorphous resin particle dispersion A1) While further stirring the resin solution A1, 90.0 parts by mass of ion-exchanged water was gradually added, followed by phase inversion emulsification and removal of the solvent, to obtain an amorphous resin particle dispersion A1 (solids concentration: 25% by mass) containing an amorphous polyester resin. The volume average particle size of the resin particles in the amorphous resin particle dispersion A1 was 0.19 μm.

[0369] (Synthesis of crystalline polyester C1) 1,10-Decanedicarboxylic acid 230.0 parts by mass 1,9-nonanediol 168.0 parts by mass Dibutyltin oxide 0.1 parts by mass

[0370] The above materials were placed in a heated and dried two-necked flask, and nitrogen gas was introduced into the container to maintain an inert atmosphere and raise the temperature while stirring. Then, stirring was performed at 170°C for 6 hours. Then, while continuing to stir, the temperature was gradually raised to 230°C under reduced pressure and maintained for another 3 hours. When the mixture became viscous, it was air-cooled to stop the reaction, and crystalline polyester C1 was synthesized. The weight average molecular weight (Mw) of crystalline polyester C1 was 36,700 and the melting point was 73.0°C.

[0371] (Preparation of Crystalline Resin Particle Dispersion C1) Crystalline resin particle dispersion C1 (solid content: 25.0% by mass) containing a crystalline polyester resin was obtained in the same manner as in preparation of amorphous resin particle dispersion A1, except that the resin used was crystalline polyester C1. The volume average particle size of the resin particles in the crystalline resin particle dispersion C1 was 0.19 μm.

[0372] (Preparation of wax dispersion W1) Behenyl behenate 50.0 parts by mass Anionic surfactant (Daiichi Kogyo Seiyaku Co., Ltd., Neogen RK) 0.3 parts by mass Ion-exchanged water 150.0 parts by mass

[0373] The above materials were mixed and heated to 95°C, and dispersed using a homogenizer (Ultra Turrax T50, manufactured by IKA). Then, the mixture was dispersed using a Manton-Gaulin high-pressure homogenizer (manufactured by Gaulin) to obtain a wax dispersion W1 (solid content concentration: 25.0% by mass). The volume average particle size of the wax particles in the wax dispersion W1 was 0.22 μm. Behenyl behenate is a release agent and has a melting point of 73°C.

[0374] (Preparation of magnetic material M1) Fe 2+50 L of an aqueous solution of ferrous sulfate containing 2.0 mol / L was mixed with 55 L of an aqueous solution of sodium hydroxide containing 4.0 mol / L, and stirred to obtain an aqueous solution of ferrous salt containing ferrous hydroxide colloid. This aqueous solution was kept at 85°C and an oxidation reaction was carried out while blowing in air at 20.0 L / min, to obtain a slurry containing core particles.

[0375] The obtained slurry was filtered and washed using a filter press, and the core particles were dispersed in water again. Sodium silicate was added to the obtained reslurry in an amount of 0.20% by mass (calculated as silicon) based on the total mass of the core particles, and the pH of the slurry was adjusted to 6.0. The mixture was stirred to obtain magnetic iron oxide particles having a silicon-rich surface.

[0376] The obtained slurry was filtered with a filter press, washed, and reslurried with ion-exchanged water. 500.0 parts by mass (10.0% by mass relative to magnetic iron oxide) of ion-exchange resin SK110 (manufactured by Mitsubishi Chemical Corporation) was added to this reslurry (solid content 50.0 parts by mass / L) and stirred for 2 hours to perform ion exchange. Thereafter, the ion-exchange resin was removed by filtration with a mesh, filtered and washed with a filter press, dried and crushed to obtain magnetic material M1 with a number-average primary particle size of 0.21 μm.

[0377] (Preparation of magnetic dispersion M1) Magnetic material M1 25.0 parts by mass Ion-exchanged water 75.0 parts by mass The above materials were mixed and dispersed for 10 minutes at 8000 rpm using a homogenizer (Ultra Turrax T50, manufactured by IKA Corporation) to obtain magnetic material dispersion liquid M1. The volume average particle size of the magnetic material in the magnetic material dispersion was 0.23 μm.

[0378] (Preparation of toner base particle dispersion 1) Amorphous resin particle dispersion A1 (solids concentration: 25.0% by mass) 150.0 parts by mass Crystalline resin particle dispersion C1 (solid content concentration: 25.0% by mass) 45.0 parts by mass Wax dispersion W1 (solid content: 25.0% by mass) 15.0 parts by mass Magnetic dispersion M1 (solid content concentration: 25.0% by mass) 105.0 parts by mass

[0379] The above materials were placed in a beaker, and the total mass of water was adjusted to 250 parts by mass, and the temperature was adjusted to 30.0° C. Then, the materials were mixed by stirring at 5000 rpm for 1 minute using a homogenizer (IKA Ultra Turrax T50). Furthermore, 10.0 parts by mass of a 2.0% by mass aqueous solution of magnesium sulfate was gradually added as a flocculant. The raw material dispersion was transferred to a polymerization kettle equipped with a stirrer and a thermometer, and the mixture was heated to 50.0°C with a mantle heater and stirred to promote the growth of aggregated particles. After 60 minutes had elapsed, 200.0 parts by mass of a 5.0% by mass aqueous solution of ethylenediaminetetraacetic acid (EDTA) was added to prepare a flocculated particle dispersion. Next, the aggregated particle dispersion was adjusted to pH 8.0 using a 0.1 mol / L aqueous sodium hydroxide solution, and then the aggregated particle dispersion 1 was heated to 80.0° C. and left for 180 minutes to allow the aggregated particles to coalesce. After 180 minutes had elapsed, toner base particle dispersion liquid 1 in which the toner base particles were dispersed was obtained.

[0380] (Preparation of toner base particles 1) The toner base particle dispersion 1 was cooled to 40°C or less at a temperature decreasing rate of 300°C / min, filtered, and washed with ion-exchanged water. When the conductivity of the filtrate became 50 mS / m or less, the toner base particles that had become cake-like were taken out.

[0381] Next, the cake-like toner base particles were placed in ion-exchanged water in an amount 20 times the mass of the toner base particles, stirred with a three-one motor, and when the toner base particles were sufficiently loosened, filtered again and washed with water for solid-liquid separation. The resulting cake-like toner base particles were crushed in a sample mill and dried in an oven at 40°C for 24 hours. The resulting powder was further crushed in a sample mill and further vacuum dried in an oven at 50°C for 5 hours to obtain toner base particles 1.

[0382] <Preparation of toner base particles 2> (Preparation of amorphous resin particle dispersion B1) (1) First-stage polymerization A 5L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device was charged with 8.0 parts by mass of sodium dodecyl sulfate and 3000.0 parts by mass of ion-exchanged water, and the internal temperature of the reaction vessel was raised to 80° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream. After the temperature was raised, an aqueous solution in which 10.0 parts by mass of potassium persulfate was dissolved in 200 parts by mass of ion-exchanged water was added to the resulting mixture, and the temperature of the resulting mixture was again raised to 80° C. A monomer mixture 1 having the following composition was added dropwise to the mixture over 1 hour, and the mixture was heated and stirred at 80° C. for 2 hours to polymerize, thereby preparing a dispersion (b1) of resin particles.

[0383] (Monomer mixture 1) Styrene 480.0 parts by mass n-Butyl acrylate 250.0 parts by mass Methacrylic acid 68.0 parts by mass

[0384] (2) Second stage polymerization A solution of 7.0 parts by mass of sodium polyoxyethylene (2) dodecyl ether sulfate dissolved in 3000.0 parts by mass of ion-exchanged water was charged into a 5L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device. After heating the solution to 80°C, 80.0 parts by mass of resin particle dispersion (b1) (solid content equivalent) and monomer mixture 2 in which monomers and a release agent having the following composition were dissolved at 90°C were added, and the mixture was mixed and dispersed for 1 hour using a mechanical disperser CLEARMIX (registered trademark, manufactured by M-Technique Co., Ltd.) with a circulation path to obtain a dispersion containing emulsified particles (oil droplets).

[0385] (Monomer mixture 2) Styrene 285.0 parts by mass n-Butyl acrylate 95.0 parts by mass Methacrylic acid 20.0 parts by mass n-Octyl-3-mercaptopropionate 8.0 parts by mass Behenyl behenate 190.0 parts by mass

[0386] Next, an initiator solution in which 6.0 parts by mass of potassium persulfate was dissolved in 200.0 parts by mass of ion-exchanged water was added to this dispersion, and the resulting dispersion was polymerized by heating and stirring at 84°C for 1 hour to obtain a dispersion of resin particles (b2).

[0387] (3) Third-stage polymerization Further, 400.0 parts by mass of ion-exchanged water was added to the resin particle dispersion (b2) and thoroughly mixed, and then a solution of 11.0 parts by mass of potassium persulfate dissolved in 400.0 parts by mass of ion-exchanged water was added to the obtained dispersion, and monomer mixture 3 having the following composition was added dropwise over 1 hour at a temperature condition of 82° C. After completion of the dropwise addition, the dispersion was heated and stirred for 2 hours to polymerize, and then cooled to 28° C. to obtain amorphous resin particle dispersion B1 containing a vinyl resin (styrene-acrylic resin).

[0388] (Monomer mixture 3) Styrene 307.0 parts by mass n-Butyl acrylate 147.0 parts by mass Methacrylic acid 52.0 parts by mass n-Octyl-3-mercaptopropionate 8.0 parts by mass

[0389] (Preparation of toner base particle dispersion 2) Into a reaction vessel equipped with a stirrer, a temperature sensor, and a cooling tube, 288.0 parts by mass of amorphous resin particle dispersion (B1) (solid content equivalent) and 2000.0 parts by mass of ion-exchanged water were added, and then a 5 mol / L aqueous sodium hydroxide solution was added to adjust the pH to 10 (measurement temperature 25° C.). Furthermore, 150.0 parts by mass of magnetic material dispersion M1 (solid content equivalent) was added to obtain toner base particle dispersion 2.

[0390] (Preparation of toner base particles 2) An aqueous solution of 30.0 parts by mass of magnesium chloride as an aggregating agent dissolved in 60.0 parts by mass of ion-exchanged water was added to the toner base particle dispersion 2 over 10 minutes under stirring at 30° C. The resulting mixture was heated to 80° C., and 75.0 parts by mass of crystalline resin particle dispersion C1 (solid content equivalent) was added to the mixture over 10 minutes to promote aggregation.

[0391] The particle size of the particles associated in this mixture was measured using a Coulter Multisizer 3 (manufactured by Beckman Coulter, Inc.). When the volume-based median diameter d50 of the particles reached 6.0 μm, an aqueous solution of 190.0 parts by mass of sodium chloride dissolved in 760.0 parts by mass of ion-exchanged water was added to stop particle growth. Furthermore, the mixture was heated to 80° C. and stirred to promote fusion of the particles.

[0392] Thereafter, using an FPIA-3000 (manufactured by Sysmex) device for measuring the average circularity of toner particles (HPF detection number: 4000 particles), the particles were cooled to 30° C. at a cooling rate of 5° C. / min when the average circularity reached 0.957.

[0393] Next, the toner cake was subjected to solid-liquid separation and dehydrated, and redispersed in ion-exchanged water. The solid-liquid separation was repeated three times to wash the toner cake, and then dried at 40° C. for 24 hours to obtain toner base particles 2.

[0394] <Preparation of toner base particles 3> (Preparation of Colorant Particle Dispersion) 90.0 parts by mass of sodium dodecyl sulfate was dissolved in 1600.0 parts by mass of ion-exchanged water with stirring. While stirring this solution, 420.0 parts by mass of carbon black Regal 330R (manufactured by Cabot Corporation) was gradually added. Next, a dispersion process was carried out using a stirring device Clearmix (manufactured by M Technique Co., Ltd.) to obtain a colorant particle dispersion liquid. The particle size of the colorant particles in the colorant particle dispersion was measured using a particle size distribution measuring device Nanotrack Wave (manufactured by Microtrack Bell Co., Ltd.) and was found to be 117.0 nm.

[0395] <Preparation of toner base particles 3> (Preparation of Toner Base Particle Dispersion 3) Amorphous resin particle dispersion A1 (solid content 25.0% by mass) 45.0 parts by mass Amorphous resin particle dispersion B1 (solid content 25.0% by mass) 150.0 parts by mass Wax dispersion W1 (solid content 25.0% by mass) 15.0 parts by mass Magnetic dispersion M1 (solid content 25.0% by mass) 105.0 parts by mass

[0396] Toner base particle dispersion 3 was obtained in the same manner as in toner base particle dispersion 1, except that the materials used were changed to the above materials. Next, the same steps as in the preparation of toner base particle 1 were carried out to obtain toner base particle 3.

[0397] <Preparation of Toner Base Particles 4> (Preparation of Crystalline Resin Particle Dispersion C2) Isophorone diisocyanate 1000.0 parts by mass 1,4-adipate (polyester diol consisting of 1,4-butanediol and adipic acid) 830.0 parts by mass Stearic acid 96.3 parts by weight Methyl ethyl ketone 250.0 parts by mass

[0398] The above materials were charged into a reactor equipped with a stirrer and a thermometer while introducing nitrogen. Then, a urethane reaction was carried out at 80° C. for 6 hours. Next, 2128.0 parts by mass of ion-exchanged water was added while stirring, and then the reaction system was decompressed to remove the solvent, thereby obtaining a crystalline resin particle dispersion C2 containing a crystalline polyurethane resin.

[0399] Toner base particle dispersion liquid 4 is obtained in the same manner as in toner base particle dispersion liquid 1, except that the material used is changed from crystalline resin particle dispersion liquid C1 to crystalline resin particle dispersion liquid C2. Next, the same steps as in the preparation of toner base particle 1 are carried out to obtain toner base particle 4.

[0400] [Preparation of external additives 1 to 9] <Preparation of external additives 1-9 (strontium titanate TS-1-9)> (Preparation of strontium titanate TS-4) Metatitanic acid obtained by the sulfuric acid method was bleached to remove iron, then an aqueous sodium hydroxide solution was added to adjust the pH to 9.0, and desulfurized. The solution was then neutralized to pH 5.8 with hydrochloric acid, filtered, and washed with water. Water was added to the washed cake to make a slurry of 1.85 mol / L in terms of TiO2, and hydrochloric acid was added to adjust the pH to 1.0, and the solution was peptized. 0.625 mol of this metatitanic acid was collected as TiO2 and placed in a 3L reaction vessel. Furthermore, 0.719 mol of an aqueous strontium chloride solution and an aqueous lanthanum chloride solution were added so that the SrO / LaO / TiO2 molar ratio was 1.00 / 0.18 / 1.00, and the TiO2 concentration was adjusted to 0.313 mol / L. Next, the mixture was heated to 90°C while stirring and mixing, and 296 mL of an aqueous 5 mol / L sodium hydroxide solution was added over 18 hours, and then the reaction was completed by continuing stirring at 95°C for 1 hour.

[0401] The reaction slurry was cooled to 50°C, hydrochloric acid was added until the pH reached 5.0, and stirring was continued for 1 hour. The resulting precipitate was decanted and washed, and hydrochloric acid was added to the slurry containing the precipitate to adjust the pH to 6.5, and 9.0 mass% of isobutyltrimethoxysilane was added relative to the solid content, and stirring was continued for 1 hour. Next, filtration and washing were performed, and the resulting cake was dried in the air at 120°C for 8 hours to obtain strontium titanate TS-4.

[0402] (Preparation of strontium titanate TS-1-3 and 5-7) Strontium titanates TS-1 to 3 and 5 to 7 were obtained in the same manner as in the preparation of strontium titanate TS-4, except that the preparation conditions were changed to those shown in Table I.

[0403] [Table 1]

[0404] (Preparation of strontium titanate TS-8) Strontium titanate TS-8 was obtained in the same manner as in the preparation of strontium titanate TS-4, except that the SrO / LaO / TiO2 molar ratio was changed to 1.00 / 0 / 1.00.

[0405] (Preparation of strontium titanate TS-9) Strontium titanate TS-9 was obtained in the same manner as in the preparation of strontium titanate TS-4, except that the aqueous solution of lanthanum chloride was changed to an aqueous solution of manganese chloride.

[0406] [External additive 10 (silica)] As the external additive 10, "NAX50" manufactured by Aerosil Corporation was used.

[0407] <Various measurements> The number-average primary particle size and average circularity of the obtained strontium titanates TS-1 to TS-9 were measured by the above-mentioned measuring methods, and the obtained results are shown in Table II.

[0408] [Preparation of toner particles 1 to 13] In the combinations shown in Table II, 0.95 parts by mass of an external additive was added to 100 parts by mass of the toner base particles, and mixed for 15 minutes at a stirring peripheral speed of 30 m / sec in a Henschel mixer to obtain toner particles 1 to 13. In Table II, CPES means crystalline polyester, APES means amorphous polyester, St-Ac means vinyl resin, and PU means crystalline polyurethane.

[0409] [evaluation] The obtained toner particles 1 to 13 were evaluated as follows in an environment of 30°C and 80% RH using a LaserJet Pro M12 (manufactured by Hewlett-Packard Co.) of a one-component contact development system as an evaluation device. The results are shown in Table II. In each evaluation, a score of ◯ or higher was considered to be acceptable.

[0410] (1) Low-temperature fixability A4 size high-quality paper (Nippon Paper Industries Co., Ltd., NPI high-quality, basis weight: 127.9 g / m 2 ) with a toner adhesion of 11.3 g / m 2 A solid image of 100 mm x 100 mm size was formed. At this time, images were repeatedly formed while the temperature of the fixing roller was increased in 2°C increments from 110°C to 180°C. The lowest fixing temperature at which image staining due to fixing offset was not visually confirmed was defined as the lowest fixing temperature (UO avoidance temperature), and the low-temperature fixing ability was evaluated according to the following criteria. ◎: Minimum fixing temperature is less than 175℃ 〇: Minimum fixing temperature is 175℃ or higher and less than 185℃ ×: Minimum fixing temperature is 185°C or higher

[0411] (2) Coverage For a blank sheet of paper with no printing on it, the absolute image density was measured at 20 points using a Macbeth Reflection Densitometer "RD907" (manufactured by Macbeth Co., Ltd.) and the average was taken as the blank sheet density. Next, for the white background portion of the evaluation image, the absolute image density was similarly measured at 20 points and the average was taken, and the value obtained by subtracting the blank sheet density from this average density was used as the fogging density. ◎: Fog density is less than 0.007 ○: Fog density is 0.007 or more and less than 0.010 ×: fog density is 0.010 or more

[0412] (3) Image density stability Before and after printing 1 million sheets, the A4 size high-quality paper "CF Paper (Konica Minolta, Inc., basis weight: 80.0 g / m 2 A 40% halftone image was printed on the entire surface of the paper. The reflection density of the resulting image was measured using a Macbeth reflection densitometer "RD907" (manufactured by Macbeth Co., Ltd.), and the difference in reflection density of the halftone image before and after image formation on 1 million sheets was determined. ◎: Absolute value of reflection density difference is 0.03 or less ○: Absolute value of reflection density difference is more than 0.03 and less than 0.06 ×: Absolute value of reflection density difference is more than 0.06

[0413] [Table 2]

[0414] From the results in Table II, it can be seen that the toner for developing electrostatic images of the present invention has improved low-temperature fixing property, fogging suppression, and image stability. From this, it is considered that the toner for developing electrostatic images of the present invention has improved low-temperature fixing property and fogging suppression, and further has durability, so that even if used for a long period of time, charge decay caused by exposure of the magnetic material to the surface of the toner particles is suppressed, and as a result, image density stability is improved. It is also understood that by adjusting the number-average primary particle size and average circularity of the toner for developing electrostatic images within suitable ranges, it is possible to achieve both low-temperature fixability, fogging suppression, and durability. [Explanation of symbols]

[0415] 43 Cleaner container 44 Cleaning blade 45 Electrostatic image carrier 46 Charging roller 47 Toner carrier 48 Toner supply member 49 Developing device 50 Transfer member (transfer roller) 51 Fixing unit 52 Pickup roller 53 Transfer material 54 Laser Generator 55 Toner control member 56 Fixing member 57 Toner 58 Stirring member R1~R3 ​​rotation method

Claims

1. A toner for developing an electrostatic image, comprising toner base particles containing at least a binder resin and a magnetic material, and an external additive, The binder resin contains a crystalline resin, the content of the magnetic material is within a range of 30 to 50% by mass with respect to the total mass of the toner base particles; The external additive contains strontium titanate doped with a metal element other than titanium and strontium.

2. A toner for developing electrostatic images.

2. The strontium titanate is lanthanum-doped strontium titanate.

2. The toner for developing electrostatic images according to claim 1.

3. The number average primary particle size of the strontium titanate particles is within the range of 20 to 300 nm.

3. The toner for developing electrostatic images according to claim 1 or 2.

4. The number average primary particle size of the strontium titanate particles is within the range of 20 to 100 nm. The toner for developing an electrostatic image according to any one of claims 1 to 3.

5. The average circularity of the primary particles of the strontium titanate particles is within a range of 0.82 to 0.

94. The toner for developing an electrostatic image according to any one of claims 1 to 4.

6. The crystalline resin is a crystalline polyester. The toner for developing an electrostatic image according to any one of claims 1 to 5.

7. An image forming method using a toner for developing an electrostatic image, comprising the steps of: The toner for developing electrostatic images according to any one of claims 1 to 6 is used.

1. An image forming method comprising:

Images