Electrophotography developer, electrophotographic image formation method, electrophotographic image formation device and process cartridge

Abstract

To provide electrophotography developer that makes low-temperature fixation possible, and suppresses shortening a life of photoreceptor by scratches, to be described later, occurring as a side effect of a fall in charging over time, while suppressing toner spent to a carrier surface in a long period of use, and suppressing imperfection caused by the fall therein.SOLUTION: Electrophotography developer includes: a carrier that is made of a core material particle, and a coating layer coating the core material particle; and toner. In the electrophotography developer, the toner is pulverized toner that contains at least one kind of polyester resin, aromatic petroleum resin, and hydrocarbon system wax, an additive amount of the aromatic petroleum resin is 2 pts.mass or more and 15 pts.mass or less with respect to 100 pts.mass of the toner, and the carrier is the carrier in which an internal porosity is 0.0[%] or more, and less than 2.0[%].SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic developer, an electrophotographic image forming method, an electrophotographic image forming apparatus, and a process cartridge. [Background technology]

[0002] In general, in image forming methods such as electrophotography and electrostatic photography, a developer is used to develop an electrostatic latent image formed on a latent image carrier. This developer is required to be a mixture that is appropriately charged. Generally, methods for developing electrostatic latent images are known, including a two-component development method that uses a two-component developer obtained by mixing toner and carrier, and a single-component development method that uses a single-component developer that does not contain carrier.

[0003] The two-component development method uses a carrier, which provides a large frictional charging area for the toner, and has more stable charging characteristics than the single-component development method, making it advantageous for maintaining high image quality over a long period of time. Furthermore, the two-component development method has a high toner supply capacity to the development area, so it is widely used, especially in high-speed machines. Furthermore, the aforementioned features are useful in digital electrophotography systems, which form an electrostatic latent image on a photoreceptor using a laser beam or the like and then visualize this latent image, so the two-component development method is widely used.

[0004] Carriers used in such two-component development methods have been investigated for their high durability by coating them with appropriate resin materials for the purposes of preventing toner from being spent on the carrier surface, forming a uniform carrier surface, preventing surface oxidation, preventing a decrease in humidity sensitivity, extending the life of the developer, protecting the photoreceptor from scratches or wear caused by the carrier, controlling the charge polarity or adjusting the charge amount, etc. For example, those coated with a specific resin material (Patent Document 1), those further having various additives added to the coating layer (Patent Documents 2 to 8), and those using carriers with additives attached to the surface (Patent Document 9) have been disclosed.

[0005] Furthermore, in order to respond to the trend toward low-temperature fixation of toner, attempts have been made to use polyester resins, which have excellent low-temperature fixability due to their high sharp melting properties and relatively high heat-resistant storage stability, instead of the styrene-acrylic resins that have been widely used in the past (Patent Documents 10 to 15).

[0006] Resin-coated carriers have been proposed in which conductive carbon or conductive filler is dispersed as a conductive agent in the coating layer of the carrier (for example, Patent Documents 16 to 19). Summary of the Invention [Problem to be solved by the invention]

[0007] The present inventors have conducted extensive research to solve the above problems, and have an object to provide an electrophotographic developer that is capable of low-temperature fixing, suppresses toner spent on the carrier surface during long-term use to suppress problems caused by a decrease in charge over time, and also suppresses a side effect of this, which is a shortened life due to scratches on the photoreceptor, as described below. [Means for solving the problem]

[0008] The above problems can be solved by the electrophotographic developer of the present invention described below in (1). (1) An electrophotographic developer comprising a carrier made of core particles and a coating layer covering the core particles, and a toner, the toner is a pulverized toner containing a polyester resin, an aromatic petroleum resin, and a hydrocarbon wax, the amount of the aromatic petroleum resin added is 2 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the toner, The carrier has an internal porosity of 0.0% or more and less than 2.0%. 1. An electrophotographic developer comprising: [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an electrophotographic developer which is capable of low-temperature fixing, which suppresses toner spent on the carrier surface during long-term use, thereby suppressing problems caused by a decrease in charge over time, and which also suppresses a shortened lifespan caused by scratches on the photosensitive member, which occurs as a side effect, as described below. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic view showing an example of an electrophotographic image forming apparatus according to the present invention. [Figure 2] FIG. 2 is a schematic view showing an example of a process cartridge according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in further detail below. In recent years, there has been a demand for low-temperature fixing of toner in electrophotography. This is due to the demand for higher speed and higher image quality of electrophotographic image forming apparatuses as well as energy conservation by reducing the energy required for fixing. Various studies have been conducted to improve the fixing properties of toner. For example, a method of controlling the thermal properties of the resin itself, such as the glass transition temperature (Tg) and softening temperature (T1 / 2), is known to improve the fixing performance of toner. In recent years, as mentioned above, in order to respond to the trend toward low-temperature fixing, attempts have been made to use polyester resins, which have excellent low-temperature fixing properties due to their high sharp melting properties and relatively high heat-resistant storage stability, instead of the styrene-acrylic resins that have been widely used in the past.

[0012] When toner components become spent on the carrier surface after long-term use of the developer, the carrier's charging ability decreases. When the carrier's charging ability decreases, the toner charge decreases, causing problems such as the toner scattering from the developer and contaminating the surrounding area or unstable image density. The toner components that become spent on the carrier surface are often external additives, binder resins, and waxes.

[0013] In particular, in pulverized toners produced by a pulverization method in which raw materials such as binder resin, colorant, and wax are melted and kneaded, the kneaded mixture is cooled, and then pulverized and classified, the wax is generally more easily pulverized than the binder resin and is more likely to be exposed at the pulverization interface, and also the wax generally softens at a lower temperature than the binder resin, so that wax-spent tends to occur relatively easily. If the amount of spent on the carrier surface becomes excessive, the carrier's ability to impart charge decreases, resulting in insufficient toner charging, which can cause problems such as unstable density of output images and toner scattering inside the machine and causing contamination.

[0014] Resin-coated carriers are insulated by the resin coating and no longer function as a development electrode, resulting in the disadvantage of edge effects, particularly in solid image areas. Furthermore, excessive countercharge during toner detachment increases the likelihood of carrier adhesion to non-image areas due to electrostatic development. Carrier adhesion refers to the transfer (adhesion) of carrier from the developer carrier to the photoreceptor, resulting in image defects such as white spots and, in the device, defects such as scratches caused by the carrier adhering to the photoreceptor being rubbed together with the toner by the cleaning element during the cleaning process, shortening the photoreceptor's lifespan. Scratches on the photoreceptor are particularly pronounced when the toner has high fluidity and requires a strong pressure from the cleaning element against the photoreceptor to achieve sufficient cleaning. In order to solve this problem, for example, as mentioned above, a resin-coated carrier has been proposed in which conductive carbon or conductive filler is dispersed as a conductive agent in the coating layer of the carrier.

[0015] However, the coated carrier particles tend to have lower magnetization than the so-called core particles before coating. This is because the resins and conductive agents used as coating materials do not have magnetization. If the carrier magnetization becomes too low, the magnetic binding force from the developer carrier weakens, and the carrier particles cannot withstand the Coulomb force acting in a direction that causes carrier adhesion, which is generated by the counter charge and the injected charge from the developer carrier. This also contributes to the occurrence of carrier adhesion.

[0016] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that by using a pulverized toner containing a polyester resin, an aromatic petroleum resin, and a hydrocarbon wax, in which the amount of the styrene resin or the aromatic petroleum resin added is 2 to 15 parts by mass per 100 parts by mass of the toner, and by using a carrier having an internal porosity of 0.0% to less than 2.0%, it is possible to provide an electrophotographic developer that is capable of low-temperature fixing, suppresses toner spent on the carrier surface during long-term use, thereby suppressing problems caused by a decrease in charge over time, and also suppresses a shortened lifespan due to scratches on the photoreceptor that occur as a side effect.

[0017] As mentioned above, using a polyester resin as a binder resin is effective in making a toner fixable at low temperatures. However, even when a sharp-melt polyester resin is used, when outputting images using a low-temperature fixable toner, if many sheets of output paper immediately after fixing are stacked in succession, the sheets will stick together, resulting in a problem known as paper ejection blocking. The use of a wax with a relatively high melting point is effective in suppressing paper ejection blocking. After extensive research, the present inventors have found that, among waxes with relatively high melting points, the use of hydrocarbon waxes is particularly effective in suppressing paper ejection blocking, and that the use of Fischer-Tropsch wax is particularly effective.

[0018] The toner in the present invention is a pulverized toner produced by a pulverization method. As mentioned above, in pulverized toner, wax is generally more easily pulverized than binder resin, so wax is more likely to be exposed at the pulverized interface, and wax with a relatively low softening point comes into direct contact with the carrier surface, which tends to result in wax-spent. This tendency is particularly strong with hydrocarbon wax, which is relatively prone to cracking.

[0019] The present inventors have conducted extensive research focusing on this process by which wax is exposed at the pulverization interface, and have found that by incorporating an aromatic petroleum resin, which has excellent pulverizability, as a toner constituent component, the aromatic petroleum resin portion is preferentially cracked during the toner pulverization process, thereby reducing the probability that wax will become part of the pulverization interface and reducing the amount of wax exposed, thereby significantly suppressing wax spending on the carrier surface.

[0020] On the other hand, when the amount of exposed wax decreases, the coefficient of friction between particles decreases, which tends to increase the fluidity of the toner. When the fluidity of the toner increases, the toner tends to slip through the cleaning member during the photoreceptor cleaning step in the electrophotographic development process, making it necessary to press the cleaning member firmly against the photoreceptor. In this case, if carrier particles are present on the photoreceptor due to the aforementioned carrier adhesion, this can cause damage to the photoreceptor. The more strongly the cleaning member is pressed against the photoreceptor, the greater the degree of damage to the photoreceptor, accelerating photoreceptor degradation. Deterioration of the photoreceptor due to friction scratches can cause defects such as blurred or streaked images, as well as reduced image density.

[0021] The inventors have conducted extensive research into this issue and have found that by using a carrier with low internal porosity as a developer, less carrier particles are mixed into the toner that is cleaned off the photosensitive member during the cleaning process, and the rate of deterioration of the photosensitive member is slowed down even when the aforementioned toner with high fluidity is used.

[0022] The toner in the present invention is a pulverized toner produced by a pulverization method. The pulverization method is a method for producing a toner by melting and kneading toner components such as a binder resin, a colorant, and a wax, and then cooling the kneaded mixture, followed by pulverization and classification.

[0023] The toner in the present invention contains a polyester resin. <Polyester resin> As the polyester resin, a generally known polyester resin obtained by polycondensation reaction of alcohol and carboxylic acid can be used.

[0024] Examples of the alcohol include diols, etherified bisphenols, dihydric alcohol monomers obtained by substituting these with saturated or unsaturated hydrocarbon groups having 3 to 22 carbon atoms, and trihydric or higher alcohol monomers.

[0025] Examples of the diols include ethylene glycol, polyethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-propylene glycol, neopentyl glycol, and 1,4-butenediol.

[0026] Examples of the etherified bisphenols include 1,4-bis(hydroxymethyl)cyclohexane, bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A, bisphenol A propylene oxide, and bisphenol A ethylene oxide.

[0027] Examples of the trihydric or higher alcohol monomer include sorbitol, 1,2,3,6-hexanetetrol, 1,4-salbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene. These may be used alone or in combination of two or more.

[0028] Examples of the carboxylic acid include monocarboxylic acids, divalent organic acid monomers, anhydrides of these acids, dimers of lower alkyl esters and linoleic acid, and trivalent or higher polyvalent carboxylic acid monomers.

[0029] Examples of the monocarboxylic acid include palmitic acid, stearic acid, and oleic acid.

[0030] Examples of the divalent organic acid monomer include maleic acid, fumaric acid, mesaconic acid, citraconic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, malonic acid, and those obtained by substituting these with a saturated or unsaturated hydrocarbon group having 3 to 22 carbon atoms.

[0031] Examples of the trivalent or higher polyvalent carboxylic acid monomer include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, embole trimer acid, and anhydrides of these acids. These may be used alone or in combination of two or more.

[0032] The molecular weight of the polyester resin is 3,500 or more and 5,500 or less, and preferably 4,000 or more and 4,500 or less. The molecular weight of the polyester resin can be determined from the molecular weight distribution of the THF-soluble fraction obtained by GPC (gel permeation chromatography). A calibration curve can be prepared using a standard polystyrene sample. The content of the polyester resin is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 70% by mass or more and 90% by mass or less, and more preferably 75% by mass or more and 85% by mass or less, based on the toner.

[0033] The toner of the present invention contains an aromatic petroleum resin. <Aromatic petroleum resin> The toner of the present invention contains an aromatic petroleum resin, which improves grindability and makes it possible to improve heat-resistant storage stability while maintaining low-temperature fixability. The aromatic petroleum resin is a resin synthesized using styrene, vinyltoluene, indene, and the like, which are C9 fractions of petroleum, as raw materials. Known resins can be used, and examples thereof include styrene, α-methylstyrene, β-methylstyrene, vinyltoluene, indene, and copolymers using these, such as styrene resin, α-methylstyrene resin, vinyltoluene-based resin, styrene-α-methylstyrene copolymer, and coumarone-indene resin. Styrene-based copolymers are particularly preferred, and α-methylstyrene-based copolymers are more preferred. A good example is styrene-α-methylstyrene copolymer.

[0034] The weight-average molecular weight (Mw) of the aromatic petroleum resin is preferably 2000 or more and 3500 or less. A weight-average molecular weight of 2000 or more can ensure a high spent suppression effect. Furthermore, a weight-average molecular weight of 3500 or less can ensure good grindability.

[0035] The styrene copolymer is not particularly limited, and examples thereof include styrene and its substituted polymers such as polystyrene, poly-p-styrene, and polyvinyltoluene, styrene-α-methylstyrene copolymer, styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-maleic acid copolymer, and styrene-maleic acid ester copolymer. Among these, styrene-α-methylstyrene copolymer is particularly preferred.

[0036] The glass transition temperature (Tg) of the styrene copolymer is preferably 60° C. or higher, and more preferably 65 to 85° C. When the Tg of the styrene copolymer is 60° C. or higher, the heat-resistant storage stability is also improved.

[0037] The Tg is measured using a differential scanning calorimeter (Q-200, manufactured by TA Instruments). Specifically, approximately 5.0 mg of the target sample is placed in an aluminum sample container, which is then placed on a holder unit and set in an electric furnace. The sample is then heated from -80°C to 150°C at a rate of 10°C / min in a nitrogen atmosphere, and the glass transition temperature (Tg) of the target sample is determined from the resulting DSC curve using an analysis program in the differential scanning calorimeter.

[0038] In the toner of the present invention, the content of the aromatic petroleum resin is 2 to 15 parts by mass per 100 parts by mass of the toner. By making the content 2% by mass or more, it is possible to maintain a certain level of grindability while improving the wax dispersibility, thereby improving the spent suppression effect.

[0039] Furthermore, aromatic petroleum resins disperse within the toner to improve grindability, but because they have a glass transition temperature above a certain level, they act to impair low-temperature fixability. However, by limiting the content to 15 parts by mass or less, the excellent low-temperature fixability of polyester resins can be exhibited without being impaired. More preferably, the content of the aromatic petroleum resin in the toner is 3.5% by mass or more and 9.0% by mass or less.

[0040] The toner of the present invention contains a hydrocarbon wax. <Hydrocarbon wax> Hydrocarbon waxes have a relatively high melting point and are suitable as waxes that have a high effect of suppressing paper discharge blocking. In particular, the hydrocarbon wax in the present invention preferably has a melting point of 80° C. or higher and 100° C. or lower, and more preferably has an SP value of 8.0 (cal / cm 3 ) 1 / 2 More than 8.5(cal / cm 3 ) 1 / 2 It is preferable that: By setting the melting point of the wax to 80°C or higher, not only can the paper discharge blocking property be improved but also the thermal properties can be made closer to those of the binder resin, which results in plasticizing these materials when heated and ensuring good low-temperature fixability.Furthermore, by setting the melting point of the wax to 100°C or lower, poor release properties due to insufficient wax melting when heated can be prevented, ensuring good low-temperature fixability.

[0041] The SP value of the wax is 8.0 (cal / cm 3 ) 1 / 2By setting the SP value to 8.5 (cal / cm), the dispersion of the aromatic petroleum resin can be maintained well, and it is possible to achieve both high levels of grindability and low-temperature fixability without causing fixation inhibition. 3 ) 1 / 2 By satisfying the above condition, compatibility with the aromatic petroleum resin can be prevented, and as a result, a state in which a certain amount of the aromatic petroleum resin is dispersed in the toner can be achieved, thereby ensuring good grindability.

[0042] Known hydrocarbon waxes can be used. Examples include Fischer-Tropsch wax and microcrystalline wax. Fischer-Tropsch wax is particularly preferred. Fischer-Tropsch wax has a high melting point and a sharp molecular weight distribution, and therefore has excellent heat-resistant storage stability and spent resistance.

[0043] The amount of wax added to the toner is preferably 2.5% by mass to 6.5% by mass, particularly preferably 3.5% by mass to 5.5% by mass. By setting the wax content to 3.5% by mass to 5.5% by mass, it is possible to prevent deterioration of durability due to excess wax while ensuring releasability.

[0044] The melting point of the wax can be measured by the following method. The glass transition temperature and melting point were measured under the following conditions using a thermal analysis workstation TA-60WS and a differential scanning calorimeter DSC-60 (Shimadzu Corporation). Sample container: Aluminum sample pan (with lid) Sample amount: 5 mg Reference: Aluminum sample pan (alumina 10 mg) Atmosphere: Nitrogen (flow rate 50 ml / min) Temperature rise and fall conditions: as follows Starting temperature: 20℃ Heating rate: 10℃ / min End temperature: 150℃ Hold Time: None Cooling rate: 10℃ / min End temperature: 20℃ Hold Time: None Heating rate: 10℃ / min Hold Time: None (The endothermic peak observed during this temperature rise process was taken as the melting point.) End temperature: 150℃

[0045] <Other toner materials> Other toner material components are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include colorants, resin particles, charge control agents, external additives, flowability improvers, cleaning property improvers, and magnetic materials.

[0046] -Coloring agent- As the colorant used in the toner of the present invention, for example, carbon black, lamp black, iron black, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa Yellow G, rhodamine 6C lake, chalco oil blue, chrome yellow, quinacridone, benzidine yellow, rose bengal, triarylmethane dyes, and other conventionally known dyes and pigments can be used. These can be used alone or in combination, and can also be used as black toner or full color toner. The content of the colorant is preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 20% by mass or less, based on the binder resin component of the toner.

[0047] -Charge control agent- The charge control agent is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxyamines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkylamides, phosphorus simple substance or compounds, tungsten simple substance or compounds, fluorine-based activators, metal salicylate, and metal salts of salicylic acid derivatives. Specific examples include the nigrosine dye Bontron 03, the quaternary ammonium salt Bontron P-51, the metal-containing azo dye Bontron S-34, the oxynaphthoic acid metal complex E-82, the salicylic acid metal complex E-84, and the phenolic condensate E-89 (all manufactured by Orient Chemical Industry Co., Ltd.), the quaternary ammonium salt molybdenum complexes TP-302 and TP-415, and the azo iron compound T-77 (all manufactured by Hodogaya Chemical Co., Ltd.), LRA-901, the boron complex LR-147 (manufactured by Nippon Carlit Co., Ltd.), copper phthalocyanine, perylene, quinacridone, azo pigments, and other polymeric compounds having functional groups such as sulfonic acid groups, carboxyl groups, and quaternary ammonium salts.

[0048] -External additives- The external additive is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include fatty acid metal salts such as zinc stearate and aluminum stearate, metal oxides such as titania, alumina, tin oxide, antimony oxide and titanium oxide, silica, hydrophobic silica, fluoropolymers, etc. Among these, hydrophobic silica, titania, titanium oxide and alumina are preferred.

[0049] The silica and titanium oxide are preferably surface-treated with a flowability improver, which will be described later, and used as hydrophobic silica and hydrophobic titanium oxide. Examples of the silica include R972, R974, RX200, RY200, R202, R805, and R812 (all manufactured by Nippon Aerosil Co., Ltd.), and HDK-2000 (manufactured by Clariant Co., Ltd.).

[0050] Examples of titania include P-25 (manufactured by Nippon Aerosil Co., Ltd.), STT-30, STT-65C-S (all manufactured by Titanium Kogyo Co., Ltd.), TAF-140 (manufactured by Fuji Titanium Kogyo Co., Ltd.), MT-150W, MT-500B, MT-600B, MT-150A (all manufactured by Teika Corporation).

[0051] Examples of titanium oxide include T-805 (manufactured by Nippon Aerosil Co., Ltd.), STT-30A, STT-65S-S (all manufactured by Titanium Kogyo Co., Ltd.), TAF-500T, TAF-1500T (all manufactured by Fuji Titanium Kogyo Co., Ltd.), MT-100S, MT-100T (all manufactured by Teika Corporation), and IT-S (manufactured by Ishihara Sangyo Kaisha, Ltd.).

[0052] -Flow improver- The fluidity improver is not particularly limited and can be appropriately selected depending on the purpose as long as it is capable of performing a surface treatment to increase hydrophobicity and prevent deterioration of fluidity and charging characteristics even under high humidity conditions. Examples of the fluidity improver include silane coupling agents, silylating agents, silane coupling agents having a fluorinated alkyl group, organic titanate coupling agents, aluminum coupling agents, silicone oils, and modified silicone oils.

[0053] The carrier of the present invention has an internal porosity of 0.0% or more and less than 2.0%. In order to suppress carrier adhesion, it is essential to increase the magnetic binding force that each carrier particle receives from the developer carrier. The magnetic binding force acting on the carrier particles is proportional to the magnetic moment of each carrier particle. The magnetization of the core particles (hereinafter sometimes simply referred to as the core) is responsible for much of the carrier's magnetic moment. Since the magnetization itself is determined by the composition of the core material, an effective way to increase the magnetic moment per core material particle is to make the mass of each core material particle as large as possible.

[0054] The carrier of the present invention has an internal porosity of 0.0% or more and less than 2.0%, more preferably 0.3% or more and 1.9% or less. If the internal porosity is 2.0% or more, the loss of magnetic moment per particle increases, resulting in a decrease in carrier adhesion resistance. From the viewpoint of carrier adhesion, the lower the internal porosity, the better. However, if there is no internal porosity at all, the apparent density of the carrier becomes too high, and the volume occupied by the carrier relative to the carrier mass becomes small. This makes it difficult for charge to move between carriers in the development area, and countercharge leakage may not be able to keep up when the toner is developed.

[0055] The internal porosity of the carrier is often nearly equal to the internal porosity of the core material. This is because when a coating layer is formed by commonly used methods such as dipping or spraying, almost no voids are formed in the coating layer. Therefore, the internal porosity of the carrier can be adjusted by adjusting the internal porosity of the core material. The internal porosity of the core material can be adjusted by adjusting the composition and distribution of raw materials, the firing temperature during core material production, etc.

[0056] The internal porosity of the carrier can be measured by the following method. First, the carrier is cut and a cross section is photographed. A conventionally known method, such as SEM, can be used to photograph the cross section. Next, using conventionally known image analysis software (e.g., ImageProPremier manufactured by MediaCybernetics), the area S of the outline of a single particle is obtained from the cross section photograph. Similarly, the area s of the void space inside a single particle is obtained, and the porosity of a single particle is calculated using the following formula: Porosity of 1 particle [%] = (s / S) × 100 This is carried out for 60 randomly selected grains, and the average value is taken as the internal porosity.

[0057] The apparent density of the carrier in the present invention is 2.4 g / cm 3 ] or more than 2.7[g / cm 3 It is preferable that the apparent density of the carrier is 2.7 [g / cm3 If the apparent density exceeds 2.32.4 [g / cm 3 ], the space occupied by the carrier particles in the development area will be low when developing from the developing roller to the image carrier, making it difficult for charge to move via the carrier in the development area, and abnormal images such as ghosts will be more likely to occur. 3 In a state where the density is less than [0.01], even if the internal porosity is low, a sufficient magnetic moment cannot be obtained, and carrier adhesion deteriorates. The apparent density of the carrier can be adjusted by known methods, and is particularly useful as an adjustment factor because the composition, shape, and surface roughness of the core material have a large contribution. The apparent density of the carrier was measured according to JIS-Z2504:2000.

[0058] The core particles used in the carrier of the present invention can be appropriately selected from those known for use in two-component electrophotographic carriers depending on the purpose. In particular, Cu-Zn ferrite is preferred because it is easy to keep the internal porosity relatively low, and therefore it is easy to set the magnetic moment per carrier particle within an appropriate range from the viewpoint of carrier adhesion resistance.

[0059] The coating layer preferably contains conductive particles for the purpose of adjusting the resistance. The conductive particles may be any known material, such as carbon black, tin oxide doped with tungsten, indium, phosphorus, or any of their oxides, or inorganic fine particles such as alumina or titania on which tin oxide doped with tungsten, indium, phosphorus, or any of their oxides is provided on the substrate surface. However, since most conductive particles are nonmagnetic, adding a large amount of conductive particles for adjusting the resistance will impair the magnetic moment of the carrier particles. Therefore, conductive particles that have high resistance adjustment ability even in small amounts are preferred, and carbon black is particularly preferred.

[0060] The coating layer may contain a resin and, if necessary, other components. The resin used in the coating layer can be a silicone resin, an acrylic resin, or a combination of these. The term "silicone resin" as used herein refers to all commonly known silicone resins, including, but not limited to, straight silicone resins consisting only of organosiloxane bonds, and silicone resins modified with alkyd, polyester, epoxy, acrylic, urethane, etc. For example, commercially available straight silicone resins include KR271, KR255, and KR152 manufactured by Shin-Etsu Chemical Co., Ltd., and SR2400, SR2406, and SR2410 manufactured by Dow Corning Toray Silicone Co., Ltd. In this case, the silicone resin can be used alone, or it can be used simultaneously with other crosslinkable components, charge amount adjusting components, etc. Further examples of modified silicone resins include KR206 (alkyd-modified), KR5208 (acrylic-modified), ES1001N (epoxy-modified), and KR305 (urethane-modified), all manufactured by Shin-Etsu Chemical Co., Ltd., and SR2115 (epoxy-modified) and SR2110 (alkyd-modified), all manufactured by Dow Corning Toray Silicone Co., Ltd.

[0061] As the condensation polymerization catalyst, known catalysts can be used, such as titanium-based catalysts, tin-based catalysts, zirconium-based catalysts, and aluminum-based catalysts.

[0062] The term "acrylic resin" as used herein refers to any resin containing an acrylic component, and is not particularly limited. Acrylic resins can be used alone, but they can also be used in combination with at least one other component that undergoes a crosslinking reaction. Examples of other components that undergo a crosslinking reaction include, but are not limited to, amino resins and acid catalysts. The amino resins referred to here include, but are not limited to, guanamine and melamine resins. The acid catalysts referred to here include any catalysts that have catalytic properties. Examples include, but are not limited to, those having reactive groups such as fully alkylated, methylol group, imino group, and methylol / imino group.

[0063] In the present invention, the composition for forming the coating layer preferably contains a silane coupling agent, which allows the conductive fine particles to be stably dispersed. The silane coupling agent is not particularly limited, but examples thereof include r-(2-aminoethyl)aminopropyltrimethoxysilane, r-(2-aminoethyl)aminopropylmethyldimethoxysilane, r-methacryloxypropyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-r-aminopropyltrimethoxysilane hydrochloride, r-glycidoxypropyltrimethoxysilane, r-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane, r-chloropropyltrimethoxysilane, hexamethyldisilazane, and r-anilino Examples thereof include propyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, r-chloropropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, allyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, dimethyldiethoxysilane, 1,3-divinyltetramethyldisilazane, and methacryloxyethyldimethyl(3-trimethoxysilylpropyl)ammonium chloride, and two or more of these may be used in combination.

[0064] Commercially available silane coupling agents include AY43-059, SR6020, SZ6023, SH6026, SZ6032, SZ6050, AY43-310M, SZ6030, SH6040, AY43-026, AY43-031, sh6062, Z-6911, sz6300, sz6075, sz6079, sz6083, sz6070, sz6072, Z-6721, AY43-004, and Z-6 187, AY43-021, AY43-043, AY43-040, AY43-047, Z-6265, AY43-204M, AY43-048, Z-6403, AY43-206M, AY43-206E, Z6341, AY43-210MC, AY43-083, AY43-101, AY43-013, AY43-158E, Z-6920, Z-6940 (manufactured by Toray Silicone Co., Ltd.), and the like.

[0065] The amount of the silane coupling agent added is preferably 0.1% by mass or more and 10% by mass or less relative to the silicone resin. If the amount of the silane coupling agent added is less than 0.1% by mass, the adhesion between the core particles or conductive fine particles and the silicone resin may decrease, causing the coating layer to fall off during long-term use. If the amount of the silane coupling agent added is more than 10% by mass, filming of the toner may occur during long-term use.

[0066] The volume average particle size of the carrier core material used in the present invention is not particularly limited, but from the viewpoint of preventing carrier adhesion and carrier scattering, a volume average particle size of 20 μm or more is preferred, and from the viewpoint of preventing the occurrence of abnormal images such as carrier streaks and preventing a decrease in image quality, a volume average particle size of 100 μm or less is preferred, and in particular, using a volume average particle size of 20 μm to 70 μm can more suitably meet the recent trend toward higher image quality. The volume average particle size can be measured, for example, using a Microtrac particle size distribution meter model HRA9320-X100 (manufactured by Nikkiso Co., Ltd.).

[0067] The carrier of the present invention can be produced, for example, by dissolving the resin or the like in a solvent to prepare a coating solution, then uniformly coating the coating solution on the surfaces of the core particles by a known coating method, drying, and then baking. Examples of the coating method include a dipping method, a spraying method, and a brush coating method. The solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples of the solvent include toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, cellosolve, and butyl acetate.

[0068] The baking method is not particularly limited and can be appropriately selected depending on the purpose. For example, it may be an external heating method or an internal heating method. The baking equipment is not particularly limited and can be appropriately selected depending on the purpose. Examples include a fixed type electric furnace, a fluidized type electric furnace, a rotary type electric furnace, a burner furnace, and an apparatus equipped with a microwave.

[0069] The average thickness of the coating layer is preferably 0.2 μm or more and 1.2 μm or less, and more preferably 0.3 μm or more and 1.0 μm or less. Here, the average thickness of the coating layer can be measured by observing the cross section of the carrier using, for example, a transmission electron microscope (TEM).

[0070] The electrophotographic image forming method of the present invention is characterized by forming an image using the developer of the present invention, and the electrophotographic image forming apparatus of the present invention is characterized by including the developer of the present invention. Specifically, the electrophotographic image forming method of the present invention includes a step of forming an electrostatic latent image on an electrostatic latent image carrier (including a charging step of charging the electrostatic latent image carrier and an exposure step of forming an electrostatic latent image on the electrostatic latent image carrier), a step of developing the electrostatic latent image formed on the electrostatic latent image carrier with the developer of the present invention to form a toner image, a step of transferring the toner image formed on the electrostatic latent image carrier to a recording medium, and a step of fixing the toner image transferred to the recording medium, and may further include other steps as necessary.

[0071] The electrophotographic image forming apparatus of the present invention comprises an electrostatic latent image carrier, charging means for charging the latent image carrier, exposure means for forming an electrostatic latent image on the latent image carrier, developing means for developing the electrostatic latent image formed on the electrostatic latent image carrier with the developer of the present invention to form a toner image, transfer means for transferring the toner image formed on the electrostatic latent image carrier to a recording medium, and fixing means for fixing the toner image transferred to the recording medium, and may further comprise other means appropriately selected as necessary, such as a charge removing means, a cleaning means, a recycling means, a control means, etc.

[0072] (Electrophotographic image forming apparatus) Next, one embodiment of a method for forming an image by the electrophotographic image forming apparatus of the present invention will be described with reference to Fig. 1. Although a printer is shown as an example of the electrophotographic image forming apparatus of this embodiment, the electrophotographic image forming apparatus is not particularly limited as long as it is capable of forming an image using toner in a copier, facsimile, multifunction machine, or the like. The electrophotographic image forming apparatus includes a paper feed section 210 , a conveying section 220 , an image forming section 230 , a transfer section 240 , and a fixing unit 250 . The paper feed section 210 includes a paper feed cassette 211 in which the paper P to be fed is stacked, and a paper feed roller 212 that feeds the paper P stacked in the paper feed cassette 211 one sheet at a time.

[0073] The conveying section 220 includes a roller 221 that conveys the paper P fed by the paper feed roller 212 toward the transfer section 240, a pair of timing rollers 222 that hold the leading end of the paper P conveyed by the roller 221 and wait, sending the paper to the transfer section 240 at a predetermined timing, and a paper discharge roller 223 that discharges the paper P with the fixed color toner image onto a paper discharge tray 224.

[0074] The image forming section 230 includes, at a predetermined interval from left to right in the drawing, an image forming unit 180Y that forms an image using a developer containing yellow toner, an image forming unit 180C that uses a developer containing cyan toner, an image forming unit 180M that uses a developer containing magenta toner, an image forming unit 180K that uses a developer containing black toner, a charger 232, and an exposure unit 233. The exposure unit 233 has a light source 233a and a polygon mirror 233b. It should be noted that when referring to any one of the image forming units (180Y, 180C, 180M, 180K), it is referred to as the image forming unit.

[0075] The developer contains toner and carrier. The four image forming units (180Y, 180C, 180M, 180K) have substantially the same mechanical configuration, except for the developer used in each unit.

[0076] Here, a premix development method may be adopted as the development method, in which a premix developer in which toner and carrier are mixed in advance is replenished. In the premix development method, the excess carrier in the developing device is discharged as excess developer. This gradually refreshes the developer in the developing device. This can extend the replacement cycle associated with developer deterioration and eliminate the effort required for developer replacement.

[0077] Transfer unit 240 includes a drive roller 241, a driven roller 242, an intermediate transfer belt 243 that can rotate counterclockwise in the drawing as the drive roller 241 is driven, primary transfer rollers (244Y, 244C, 244M, 244K) that are provided opposite photoconductor 231 with intermediate transfer belt 243 in between, and secondary opposing roller 245 and secondary transfer roller 246 that are provided opposite with intermediate transfer belt 243 in between at the position where the toner image is transferred to paper. Also includes cleaning device 236 that removes residual toner remaining on the surface of photoconductor 231.

[0078] An example of the process cartridge of the present invention is shown in Figure 2. This process cartridge (1) integrally supports a photosensitive member (2), a proximity brush-like charging means (3), a developing means (4) containing the developer of the present invention, and a cleaning means (5) having at least a cleaning blade, and is detachably mountable to the main body of an electrophotographic image forming apparatus. In the present invention, the above-mentioned components are integrally combined as a process cartridge, and this process cartridge can be configured to be detachably mountable to the main body of an electrophotographic image forming apparatus such as a copier or printer. [Example]

[0079] The present invention will be described below with reference to examples and comparative examples. However, the present invention is not limited to the examples exemplified here. In the following, "parts" represents parts by mass, and "%" represents % by mass.

[0080] [Toner production] (Toner Production Example 1) <Toner base particles 1> Resin 1: 75 parts polyester resin Resin 2: α-methylstyrene resin 7 parts Wax: 6 parts paraffin wax Colorant: Carbon black 11 parts Charge control agent: Azo iron compound 1 part

[0081] According to the above recipe, the toner raw materials were premixed using a Henschel mixer (FM20B, manufactured by Mitsui Miike Chemical Engineering Co., Ltd.), and then melted and kneaded at 120°C in a twin-screw kneader (PCM-30, manufactured by Ikegai Corporation). The obtained kneaded product was rolled to a thickness of 2.7 mm using a roller, then cooled to room temperature using a belt cooler, and coarsely pulverized to 200 μm to 300 μm using a hammer mill. Next, the mixture was finely pulverized using a supersonic jet pulverizer, Labojet (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and then classified using an air classifier (manufactured by Nippon Pneumatic Mfg. Co., Ltd., MDS-I) while appropriately adjusting the louver opening so that the weight average particle size was 5.8 μm±0.2 μm, thereby obtaining [toner base particle 1].

[0082] <External additive treatment> To 100 parts of [Toner Base Particles 1], 1 part of hydrophobic silica was added as an external additive, and the mixture was stirred and mixed in a Henschel mixer to subject [Toner Base Particles 1] to external additive treatment, thereby producing [Toner 1]. The content of Resin 2 in 100 parts of [Toner 1] was 7 parts.

[0083] (Toner Production Example 2) Toner 2 was obtained in the same manner as in Toner Production Example 1, except that Resin 2 was changed to a coumarone-indene resin.

[0084] (Toner Production Example 3) Toner 3 was obtained in the same manner as in Toner Production Example 1, except that Resin 2 was changed to a vinyl toluene-based resin.

[0085] (Toner Production Example 4) Toner 4 was obtained in the same manner as in Toner Production Example 1, except that Resin 1 was changed to a styrene acrylic resin.

[0086] (Toner Production Example 5) Toner 5 was obtained in the same manner as in Toner Production Example 1, except that the amount of Resin 2 in Toner Production Example 1 was changed to 15 parts (14 parts per 100 parts of toner).

[0087] (Toner Production Example 6) Toner 6 was obtained in the same manner as in Toner Production Example 1, except that the amount of Resin 2 was changed to 18 parts (16 parts per 100 parts of toner).

[0088] (Toner Production Example 7) Toner 7 was obtained in the same manner as in Toner Production Example 1, except that the amount of Resin 2 was changed to 3 parts (3 parts per 100 parts of toner).

[0089] (Toner Production Example 8) Toner 8 was obtained in the same manner as in Toner Production Example 1, except that the amount of Resin 2 was changed to 1 part (1 part per 100 parts of toner).

[0090] (Toner Production Example 9) Toner 9 was obtained in the same manner as in Toner Production Example 1, except that Resin 2 was changed to an isoprene resin (C5 petroleum resin).

[0091] (Toner Production Example 10) Toner 10 was obtained in the same manner as in Toner Production Example 1, except that the wax was changed to carnauba wax (natural wax).

[0092] (Toner Production Example 11) Toner 11 was obtained in the same manner as in Toner Production Example 1, except that the wax was changed to Fischer-Tropsch wax.

[0093] (Toner Production Example 12) Toner 12 was obtained in the same manner as in Toner Production Example 11, except that Resin 2 was changed to a styrene-α-methylstyrene copolymer.

[0094] The composition of the resulting toner is shown in Table 1. In Table 1, the value of "number of parts of resin 2 per 100 parts of toner" indicates the number of parts of resin 2 per 100 parts of toner.

[0095] [Table 1]

[0096] [Creating the carrier] (Carrier manufacturing example 1) <Core material 1> Mn ferrite Internal porosity: 1.0[%], apparent density: 2.2[g / cm] 3 ] <Resin liquid 1> Silicone resin solution (solid content 40%) 2000 parts Aminosilane (solid concentration: 100%) 30 parts Tungsten oxide-doped tin oxide-coated alumina 1200 parts 6,000 parts toluene The materials for resin liquid 1 were dispersed in a homomixer for 10 minutes to prepare a coating layer forming liquid. The coating layer forming liquid of resin liquid 1 was applied to the core material surface at a rate of 30 g / min in an atmosphere of 55°C using a Spira Coater (manufactured by Okada Seiko Co., Ltd.) so that the thickness would be 0.8 μm, and then dried. The layer thickness was adjusted by adjusting the amount of liquid. The obtained carrier was baked in an electric furnace at 150°C for 1 hour, and after cooling, it was crushed using a sieve with 100 μm openings to obtain [carrier 1].

[0097] (Carrier manufacturing example 2) Carrier 2 was obtained in the same manner as in Carrier Production Example 1, except that Core Material 1 was changed to Core Material 2 described below. <Core material 2> Mn ferrite Internal porosity: 1.9[%], apparent density: 2.2[g / cm] 3 ]

[0098] (Carrier manufacturing example 3) Carrier 3 was obtained in the same manner as in Carrier Production Example 1, except that Core Material 1 was changed to Core Material 3 described below. <Core material 3> Mn ferrite Internal porosity: 2.2[%], apparent density: 2.1[g / cm] 3 ]

[0099] (Carrier manufacturing example 4) Carrier 4 was obtained in the same manner as in Carrier Production Example 1, except that Core Material 1 was changed to Core Material 4 below. <Core material 4> Mn ferrite Internal porosity: 0.1[%], apparent density: 2.3[g / cm] 3 ]

[0100] (Carrier manufacturing example 5) Carrier 5 was obtained in the same manner as in Carrier Production Example 1, except that Core Material 1 was changed to Core Material 5 described below. <Core material 5> Mn ferrite Internal porosity: 1.8[%], apparent density: 2.4[g / cm] 3 ]

[0101] (Carrier manufacturing example 6) Carrier 6 was obtained in the same manner as in Carrier Production Example 1, except that Core Material 1 was changed to Core Material 6 described below. <Core material 6> Mn ferrite Internal porosity: 1.2[%], apparent density: 2.6[g / cm] 3 ]

[0102] (Carrier manufacturing example 7) Carrier 7 was obtained in the same manner as in Carrier Production Example 1, except that Core Material 1 was changed to Core Material 7 below. <Core material 7> Mn ferrite Internal porosity: 0.9[%], apparent density: 2.7[g / cm] 3 ]

[0103] (Carrier manufacturing example 8) Carrier 8 was obtained in the same manner as in Carrier Production Example 1, except that Core Material 1 was changed to Core Material 8 below. <Core material 8> Mn ferrite Internal porosity: 0.5[%], apparent density: 2.9[g / cm] 3 ]

[0104] (Carrier manufacturing example 9) [Carrier 9] was obtained in the same manner as in Carrier Production Example 6, except that Resin Liquid 1 was changed to Resin Liquid 2 below. <Resin liquid 2> Silicone resin solution (solid content 40%) 2000 parts Aminosilane (solid concentration: 100%) 30 parts Carbon black 300 parts 6,000 parts toluene

[0105] (Carrier manufacturing example 10) Carrier 10 was obtained in the same manner as in Carrier Production Example 9, except that Core Material 6 was changed to Core Material 9 described below. <Core material 9> Cu-Zn ferrite Internal porosity: 0.6[%], apparent density: 2.7[g / cm] 3 ]

[0106] Table 2 shows the internal porosity and apparent density of the core material and carrier of each of the obtained carriers.

[0107] [Table 2]

[0108] [Example 1] Five parts of [Toner 1] obtained in Toner Production Example and 95 parts of [Carrier 1] obtained in Carrier Production Example 1 were mixed in a mixer for 10 minutes to prepare [Developer 1]. The developer was set in a digital full-color printer (Ricoh Co., Ltd., MP6503) that had been modified to allow the fixing temperature to be changed, and the pressure strength of the cleaning member adjusted to allow for problem-free cleaning, and an evaluation was conducted with the initial developer. In addition, 100,000 images were printed using a character chart with an image area of ​​10% at the default fixing temperature specifications, and the developer (aged developer) was evaluated.

[0109] <Low temperature fixability> Before printing 100,000 images, the adhesion amount was 0.4 mg / cm 2 The solid image was output on paper (Ricoh Type 6200) in 5°C increments of the fixing temperature through exposure, development, and transfer processes, and the minimum fixing temperature was measured by visually determining whether cold offset occurred. The minimum fixing temperature was evaluated based on the following evaluation criteria. (Evaluation criteria) ◎: Less than 130℃ ○: 130℃ or higher, less than 140℃ △: 140℃ or higher, less than 150℃ ×: 150℃ or higher

[0110] <Charge reduction amount> The amount of charge reduction was evaluated before and after 100,000 image outputs. First, a sample (initial agent) was triboelectrically charged by mixing 95% initial carrier and 5% toner by mass, and the charge was measured using a standard blow-off method (TB-200, manufactured by Toshiba Chemical Corporation). This value was taken as the initial charge amount. Next, the toner was removed from the developer after image output using the blow-off device, and new toner was mixed with the resulting developer at a ratio of 95% carrier and 5% toner. This sample was triboelectrically charged in the same manner as the initial carrier, and the charge amount was measured in the same manner as the initial carrier. The difference from the initial charge amount was taken as the charge loss. The target value for the charge loss width was less than 10.0 μC / g. The charge loss amount was evaluated based on the following evaluation criteria. (Evaluation criteria) ◎: Less than 4.0 μC / g ○: 4.0 μC / g or more, less than 6.0 μC / g □: 6.0 μC / g or more, less than 8.0 μC / g △: 8.0 μC / g or more, less than 10.0 μC / g ×: 10.0 μC / g or more

[0111] <Time-lapse images> After printing 100,000 sheets, the images were visually observed and evaluated for blurred images, streaked images, and reduction in image density based on the following evaluation criteria. (Evaluation criteria) ◎: Very good ○: Good △: Acceptable ×: Unacceptable level for practical use

[0112] <Paper ejection blocking> Print a 3cm x 15cm rectangular solid image on PPC paper type 6000<70W>A4 T-line (manufactured by Ricoh Co., Ltd.) with a toner adhesion of 0.85mg / cm 2The image was formed as shown in the figure, and 500 sheets were output continuously on one side. The fixing temperature was controlled so that it was centered around the cold offset temperature + 20°C. The 500 output images were left stacked for 1 hour, and then the adhesion of the images to each other was evaluated based on the following evaluation criteria. (Evaluation criteria) ⊚: There is absolutely no sticking of the sheets of paper together. ○: The sheets of paper are slightly stuck together, but they peel off easily and there is no problem with the image after peeling. △: The sheets of paper are slightly stuck together and make some noise when peeled off, but there is no problem with the image when peeled off. ×: The sheets of paper stick together, and the image or the paper is damaged when peeled off.

[0113] <Heat-resistant storage stability> 10 g of the toner used in each of the developers of the examples was placed in a 30 ml screw vial, tapped 100 times with a tapping machine, and then stored in a thermostatic chamber at 50°C for 24 hours. After returning to room temperature, the penetration was measured with a penetration tester, and the heat-resistant storage stability was evaluated based on the following evaluation criteria. (Evaluation criteria) ◎: Penetration ○: 20mm or more □: 15mm or more and less than 20mm △: 10mm or more and less than 15mm ×: Less than 10 mm

[0114] <Ghost> A solid image was printed using the initial developer, and the difference in image density between the leading edge of the image and the area one revolution behind the developing roller was visually observed, and ghosting was evaluated based on the following evaluation criteria. ◎: Very good ○: Good △: Acceptable ×: Unacceptable level for practical use

[0115] [Examples 2 to 15, Comparative Examples 1 to 6] Evaluations were carried out in the same manner as in Example 1, except that developers 2 to 21 were prepared in the combinations shown in Table 3 using [Toner 1] to [Toner 12] and [Carrier 1] to [Carrier 10].

[0116] Table 3 shows the properties of the toner and carrier in Developers 1 to 21, and Table 4 shows the evaluation results of Developers 1 to 21.

[0117] [Table 3]

[0118] [Table 4]

[0119] The present invention includes, for example, the following aspects. (1) An electrophotographic developer comprising a carrier made of core particles and a coating layer covering the core particles, and a toner, the toner is a pulverized toner containing a polyester resin, an aromatic petroleum resin, and a hydrocarbon wax, the amount of the aromatic petroleum resin added is 2 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the toner, The carrier has an internal porosity of 0.0% or more and less than 2.0%. 1. An electrophotographic developer comprising: (2) The electrophotographic developer according to (1) above, wherein the hydrocarbon wax is a Fischer-Tropsch wax. (3) The apparent density of the carrier is 2.4 [g / cm 3 ] or more than 2.7[g / cm 3 The electrophotographic developer according to (1) or (2), wherein: (4) The electrophotographic developer according to any one of (1) to (3) above, wherein the coating layer contains carbon black. (5) The electrophotographic developer according to any one of (1) to (4) above, wherein the core particles are formed of Cu-Zn ferrite. (6) The electrophotographic developer according to any one of (1) to (5) above, wherein the aromatic petroleum resin is a styrene resin. (7) The electrophotographic developer according to any one of (1) to (6) above, wherein the styrene-based resin is a styrene-α-methylstyrene copolymer. (8) an electrostatic latent image forming step of forming an electrostatic latent image on an electrostatic latent image carrier; a developing step of developing the electrostatic latent image with the electrophotographic developer according to any one of (1) to (6) above to form a toner image; a transfer step of transferring the toner image onto a recording medium; a fixing step of fixing the transferred image transferred onto the recording medium, Electrophotographic image forming method. (9) an electrostatic latent image carrier; an electrostatic latent image forming means for forming an electrostatic latent image on the electrostatic latent image carrier; a developing means having a developer for developing the electrostatic latent image formed on the electrostatic latent image carrier to form a visible image, The developer is the electrophotographic developer according to any one of (1) to (6) above. Electrophotographic image forming apparatus characterized in that: (10) A process cartridge comprising the electrophotographic developer according to any one of (1) to (6) above. [Explanation of symbols]

[0120] 1 Process cartridge 2 Photoreceptor 3. Charging means 4. Developing methods 5 Cleaning Method 160Y Sub Hopper (Yellow) 160C Sub Hopper (Cyan) 160M Sub Hopper (Magenta) 160K Sub Hopper (Black) 180Y Image Forming Unit (Yellow) 180C Image Forming Unit (Cyan) 180M Image Forming Unit (Magenta) 180K Image Forming Unit (Black) 200 Electrophotographic image forming apparatus 210 Paper feed section 211 Paper cassette 212 Paper feed roller 220 Conveyor 221 Laura 222 Timing roller 223 Paper ejection roller 224 Paper output tray 230 Image creation section 231Y Photoconductor drum (yellow) 231C Photoconductor drum (cyan) 231M Photoconductor Drum (Magenta) 231K Photoconductor Drum (Black) 232Y Charger (Yellow) 232C Charger (cyan) 232M Charger (Magenta) 232K Charger (Black) 233 Exposure device 233a light source 233bY Polygon Mirror (Yellow) 233bC Polygon Mirror (Cyan) 233bM Polygon Mirror (Magenta) 233bK Polygon Mirror (Black) 234Y Toner Bottle (Yellow) 234C Toner Bottle (Cyan) 234M Toner Bottle (Magenta) 234K Toner Bottle (Black) 236Y Cleaning Device (Yellow) 236C Cleaner (cyan) 236M Cleaner (Magenta) 236K Cleaner (Black) 240 Transcription Unit 241 Drive roller 242 driven roller 243 Intermediate transfer belt 244 Primary transfer roller 244Y Primary Transfer Roller (Yellow) 244C Primary transfer roller (cyan) 244M Primary Transfer Roller (Magenta) 244K Primary Transfer Roller (Black) 245 Secondary opposing roller 246 Secondary transfer roller 250 Fixing unit 251 Fixing belt 252 pressure roller L Laser P paper [Prior art documents] [Patent documents]

[0121] [Patent Document 1] Japanese Patent Application Publication No. 58-108548 [Patent Document 2] Japanese Patent Application Publication No. 54-155048 [Patent Document 3] Japanese Patent Application Publication No. 57-40267 [Patent Document 4] Japanese Patent Application Publication No. 58-108549 [Patent Document 5] Japanese Patent Application Publication No. 59-166968 [Patent Document 6] Special Publication No. 1-19584 [Patent Document 7] Special Publication No. 3-628 [Patent Document 8] Japanese Patent Application Publication No. 6-202381 [Patent Document 9] Japanese Patent Application Publication No. 5-273789 [Patent Document 10] Japanese Patent Application Publication No. 60-90344 [Patent Document 11] Japanese Patent Application Publication No. 15755 / 1983 [Patent Document 12] Japanese Patent Application Publication No. 2-82267 [Patent Document 13] Japanese Patent Application Publication No. 3-229264 [Patent Document 14] Japanese Patent Application Publication No. 3-41470 [Patent Document 15] Special Publication No. 11-305486 [Patent Document 16] Japanese Patent Publication No. 56-75659 [Patent Document 17] Special Publication No. 4-360156 [Patent Document 18] Special Publication No. 5-303238 [Patent Document 19] Special Publication No. 11-174740

Claims

1. An electrophotographic developer comprising a carrier including core particles and a coating layer that coats the core particles, and a toner, the toner is a pulverized toner containing a polyester resin, an aromatic petroleum resin, and a hydrocarbon wax, the amount of the aromatic petroleum resin added is 2 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the toner; The carrier has an internal porosity of 0.0% or more and less than 2.0%.

1. An electrophotographic developer comprising:

2. 2. The electrophotographic developer according to claim 1, wherein the hydrocarbon wax is a Fischer-Tropsch wax.

3. The apparent density of the carrier is 2.4 [g / cm ３ ] or more 2.7 [g / cm ３ 3. The electrophotographic developer according to claim 1, wherein the total molecular weight of the developer is 100 or less.

4. 3. The electrophotographic developer according to claim 1, wherein the coating layer contains carbon black.

5. 3. The electrophotographic developer according to claim 1, wherein the core particles are formed of Cu-Zn ferrite.

6. 3. The electrophotographic developer according to claim 1, wherein the aromatic petroleum resin is a styrene resin.

7. 7. The electrophotographic developer according to claim 6, wherein the styrene-based resin is a styrene-α-methylstyrene copolymer.

8. an electrostatic latent image forming step of forming an electrostatic latent image on an electrostatic latent image carrier; a developing step of developing the electrostatic latent image with the electrophotographic developer according to claim 1 or 2 to form a toner image; a transfer step of transferring the toner image onto a recording medium; a fixing step of fixing the transferred image transferred onto the recording medium, Electrophotographic image forming method.

9. an electrostatic latent image carrier; an electrostatic latent image forming means for forming an electrostatic latent image on the electrostatic latent image carrier; a developing means having a developer for developing the electrostatic latent image formed on the electrostatic latent image carrier to form a visible image, The developer is the electrophotographic developer according to claim 1 or 2. Electrophotographic image forming apparatus characterized in that:

10. A process cartridge comprising the electrophotographic developer according to claim 1 or 2.

Images