Magnetic one-component toner and image forming apparatus using the same

Abstract

The present invention provides a magnetic single-component toner that maintains high image density over a long period of time and does not cause image fogging, in a magnetic single-component development method using a non-contact regulated blade, and an image forming apparatus using the same. [Solution] The magnetic one-component toner consists of toner particles comprising toner matrix particles and an external additive attached to the surface of the toner matrix particles. The toner matrix particles include at least a binder resin and magnetic powder. The external additive includes wet silica particles and conductive inorganic particles. The wet silica particles are treated with a hydrophobic treatment agent whose surface consists of long-chain fatty acid esters with 18 or more carbon atoms. The conductive inorganic particles are treated with a hydrophobic treatment on their surface. The volume resistivity of the wet silica particles is 1.0E+7 [Ω·cm] or more and 1.0E+10 [Ω·cm] or less.

Description

Technical Field

[0001] The present invention relates to a magnetic single-component toner and an image forming apparatus using a magnetic single-component development method using the magnetic single-component toner.

Background Art

[0002] Generally, in the electrophotographic method, after the surface of the electrostatic latent image carrier is charged by corona discharge or the like, it is exposed by a laser or the like to form an electrostatic latent image. The formed electrostatic latent image is developed with toner to form a toner image. Further, the formed toner image is transferred to a recording medium to obtain a high-quality image.

[0003] As methods for developing an electrostatic latent image with toner, a magnetic single-component development method using only a magnetic toner and a two-component development method using a two-component developer including a non-magnetic toner and a magnetic carrier are known. Since the magnetic toner is less expensive than the two-component developer, the magnetic single-component development method is widely used in monochrome printers.

[0004] In the magnetic single-component development method, when the electrical resistance of the toner is high, the charge transport property in the toner chain becomes low, so that the charge distribution becomes broad and the developability deteriorates. In order to solve this problem, it is necessary to lower the electrical resistance of the toner.

[0005] Patent Document 1 discloses a magnetic single-component development method in which silica coated with a titanate-based coupling agent (long-chain fatty acid ester) is added to the toner and the same silica is dispersed in a toner application blade in a magnetic single-component development method using a toner application blade. In the configuration of Patent Document 1, when a contact-type toner application blade is used, adhesion of silica in the toner to the toner application blade is prevented without degrading the charging characteristics of the toner.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] When the method described in Patent Document 1 is applied to a magnetic single-component developing system using a non-contact regulated blade, toner containing only low-resistance silica treated with a titanate coupling agent suffers from insufficient low-resistance toner. This results in low charge propagation within the toner chain, a broadened charge distribution, and consequently, reduced developability. Furthermore, at high process linear speeds, the broadening of the charge distribution and the resulting decrease in developability become even more pronounced.

[0008] In view of the above problems, the present invention aims to provide a magnetic single-component toner that maintains high image density over a long period of time and does not cause image fogging, and an image forming apparatus using the same. [Means for solving the problem]

[0009] To achieve the above objective, the first configuration of the present invention is a magnetic one-component toner comprising toner particles containing toner matrix particles and an external additive attached to the surface of the toner matrix particles. The toner matrix particles contain at least a binder resin and magnetic powder. The external additive contains wet silica particles and conductive inorganic particles. The wet silica particles are treated on the surface with a hydrophobic treatment agent consisting of a long-chain fatty acid ester having 18 or more carbon atoms. The conductive inorganic particles are treated on the surface with a hydrophobic treatment. The volume resistivity of the wet silica particles is 1.0E+7 [Ω·cm] or more and 1.0E+10 [Ω·cm] or less. [Effects of the Invention]

[0010] According to the first configuration of the present invention, the charge distribution can be maintained within a desired range, resulting in a magnetic single-component toner that maintains high image density over a long period of time and does not produce image fogging. Therefore, it can be suitably used in magnetic single-component development methods that have a high process line speed and use a non-contact regulated blade. [Brief explanation of the drawing]

[0011] [Figure 1] Schematic cross-sectional view of an image forming apparatus 100 using the magnetic one-component toner of the present invention. [Modes for carrying out the invention]

[0012] [1. Overall configuration of the image forming apparatus] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic cross-sectional view of an image forming apparatus 100 in which the magnetic one-component toner of the present invention is used. In the image forming apparatus (e.g., a monochrome printer) 100, when printing is performed, an electrostatic latent image is formed in the image forming unit 9 within the image forming apparatus 100 based on original image data transmitted from a higher-level device (not shown), such as a personal computer, and toner is attached to the electrostatic latent image by the developing device 4 to form a toner image. Toner is supplied to the developing device 4 from the toner container 5. In the image forming apparatus 100, the image forming process on the photoreceptor drum 1 is performed while the photoreceptor drum 1 is rotated clockwise in Figure 1.

[0013] The image forming unit 9 is equipped with a charging device 2, an exposure unit 3, a developing device 4, a transfer roller 6, a cleaning device 7, and a static elimination device (not shown) along the rotation direction (clockwise) of the photoreceptor drum 1. The photoreceptor drum 1 is, for example, an aluminum drum with a photosensitive layer laminated on its surface (outer surface). The surface (outer surface) of the photoreceptor drum 1 is uniformly charged by the charging device 2. Then, an electrostatic latent image is formed on the surface that receives a light beam from the exposure unit 3, which will be described later, with the charge attenuated. The photosensitive layer is not particularly limited, but amorphous silicon (a-Si), which has excellent durability, is preferred. The linear velocity of the photoreceptor drum 1 (i.e., the process linear velocity of the image forming apparatus 100) is 330 mm / sec or more.

[0014] The charging device 2 uniformly charges the surface of the photoreceptor drum 1. The charging device 2 is a corona discharge device that discharges electricity by applying a high voltage using, for example, a thin wire as an electrode. Alternatively, a contact-type charging device may be used, in which a voltage is applied while a charging member, such as a charging roller, is in contact with the surface of the photoreceptor drum 1. The exposure unit 3 irradiates the photoreceptor drum 1 with a light beam (for example, a laser beam) based on the image data, forming an electrostatic latent image on the surface of the photoreceptor drum 1.

[0015] The developing device 4 forms a toner image by attaching toner to the electrostatic latent image on the photoreceptor drum 1. In this embodiment, a magnetic one-component toner (magnetic one-component developer) is contained in the developing device 4. The developing device 4 is a magnetic one-component jumping developing system that has a non-contact regulating blade 4b with respect to the developing roller 4a and a mechanism for charging the toner via the developing roller 4a. The cleaning device 7 is equipped with a cleaning blade 7a that makes line contact with the photoreceptor drum 1 in the longitudinal direction (the direction perpendicular to the paper surface in Figure 1), and after the toner image has been transferred to the paper, the cleaning blade 7a removes the toner remaining on the surface of the photoreceptor drum 1.

[0016] As described above, paper is transported from the paper storage unit 10 to the image forming unit 9 via the paper transport path 11 and the registration roller pair 13 at a predetermined timing, towards the photoreceptor drum 1 on which the toner image has been formed. The transfer roller 6 contacts the photoreceptor drum 1 to form a nip (transfer nip), and without disturbing the toner image formed on the surface of the photoreceptor drum 1, the toner is transferred to the paper passing through the transfer nip. Subsequently, in preparation for the formation of a new electrostatic latent image, the cleaning device 7 removes residual toner from the surface of the photoreceptor drum 1, and the static eliminator removes residual charge.

[0017] The paper onto which the toner image has been transferred is separated from the photoreceptor drum 1 and transported to the fuser unit 8, where it is heated and pressurized to fix the toner image onto the paper. The paper that has passed through the fuser unit 8 passes through the discharge roller pair 14 and is discharged to the paper discharge unit 15.

[0018] [2. Basic Toner Configuration] The following describes in detail the magnetic one-component toner of the present invention (hereinafter also simply referred to as toner) used in the image forming apparatus 100. Unless otherwise specified, the evaluation results (values ​​indicating shape or physical properties, etc.) for the powder (more specifically, toner core particles, toner matrix particles, external additives, or toner, etc.) are the number average values ​​of the values ​​measured for each of the average particles selected from the powder. Unless otherwise specified, the number average particle diameter of the powder is the number average value of the equivalent circle diameter (diameter of a circle having the same area as the projected area of ​​the particle) of the primary particles measured using a microscope. Unless otherwise specified, the measured value of the volume median diameter (D50) of the powder is the value measured using a laser diffraction / scattering particle size distribution analyzer ("LA-750" manufactured by Horiba, Ltd.). Unless otherwise specified, the measured values ​​of the acid value and hydroxyl value are the values ​​measured according to "JIS (Japanese Industrial Standards) K0070-1992". Furthermore, unless otherwise specified, the measured values ​​for number-average molecular weight (Mn) and mass-average molecular weight (Mw) are those obtained using gel permeation chromatography.

[0019] In the following, the compound name may be followed by "system" to comprehensively refer to the compound and its derivatives. When "system" is followed by a compound name to represent a polymer name, it means that the repeating unit of the polymer originates from the compound or its derivative. Also, acrylic and methacrylic may be comprehensively referred to as "(meth)acrylic". Furthermore, acryloyl (CH) 2 =CH-CO-) and methacryloyl (CH 2 =C(CH 3 The terms )-CO-) are sometimes collectively referred to as "(meth)acryloyl".

[0020] The toner according to this embodiment can be suitably used as a positively charged toner for developing electrostatic latent images. The toner of this embodiment is a powder containing a plurality of toner particles (each having a configuration described later). The toner contains magnetic powder and is used as a one-component developer.

[0021] The toner particles contained in the toner according to this embodiment include toner mother particles and external additives attached to the surface of the toner mother particles. The toner mother particles contain at least a binder resin and magnetic powder. Further, the toner mother particles may contain a colorant, a release agent, a charge control agent, etc. in the binder resin as necessary. Further, in the toner of the present invention, silica particles and conductive inorganic particles are externally added as external additives to the surface of the toner mother particles.

[0022] As the silica particles externally added to the toner of the present invention, silica particles produced in a liquid phase (wet silica particles) are used. The surface of the wet silica particles is hydrophobized with a hydrophobizing agent composed of at least a long-chain fatty acid ester having 18 or more carbon atoms.

[0023] As the conductive inorganic particles externally added to the toner of the present invention, it is preferable that they are one or more selected from alumina, titanium oxide, strontium titanate, and barium titanate. Further, in magnetic single-component jumping development, a high charge amount of the toner mother particles leads to stabilizing the charging state of the toner. Furthermore, the presence of conductive inorganic particles having high dielectric properties on the surface of the toner mother particles acts to adjust the charges between the toner particles to a uniform state. Therefore, by externally adding conductive inorganic particles to the surface of the toner mother particles, a very stable image quality can be obtained.

[0024] The toner of the present invention can sufficiently reduce the resistance of the toner particles by externally adding the wet silica particles and the conductive inorganic particles as described above to the toner mother particles. As a result, the charge transport property in the toner chain increases, and the charge amount distribution can be maintained within a certain range. Therefore, it is particularly preferably used in an image forming apparatus 100 using a magnetic single-component jumping development method as shown in FIG. 1.

[0025] [3. Materials of Toner] The binder resin, magnetic powder, colorant, release agent, charge control agent, and external additives added to the toner matrix particles, as well as the method for manufacturing the toner of the present invention, will be described below in order.

[0026] (Binding resin) The toner matrix particles constituting the toner of the present invention include a binder resin. The binder resin that can be contained in the toner matrix particles is not particularly limited as long as it is a resin that has been conventionally used as a binder resin for toner. Specific examples of binder resins include thermoplastic resins such as styrene resins, acrylic resins, styrene-acrylic resins, polyethylene resins, polypropylene resins, vinyl chloride resins, polyester resins, polyamide resins, polyurethane resins, polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. Among these resins, it is preferable to contain at least one of polyester resin and styrene-acrylic acid resin, with polyester resin being more preferable, from the viewpoint of dispersibility of the colorant in the binder resin, the electrostatic properties of the toner, and the fixation to paper. Polyester resin will be described below.

[0027] Polyester resins can be obtained by condensation polymerization or copolymerization of a divalent or trivalent or higher alcohol component with a divalent or trivalent or higher carboxylic acid component. The following alcohol and carboxylic acid components are examples of components used in the synthesis of polyester resins.

[0028] Specific examples of divalent or trivalent or higher alcohol components include diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; bisphenol A, hydrogenated bisphenol A, and polyoxyethylene Examples include bisphenols such as bisphenol A and polyoxypropylene bisphenol A; and trivalent or higher alcohols such as sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

[0029] Specific examples of divalent or trivalent or higher carboxylic acid components include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebatic acid, azelaic acid, malonic acid, or divalent alkyl or alkenyl succinic acids such as n-butylsuccinic acid, n-butenylsuccinic acid, isobutylsuccinic acid, isobutenylsuccinic acid, n-octylsuccinic acid, n-octenylsuccinic acid, n-dodecylsuccinic acid, n-dodecenylsuccinic acid, isododecylsuccinic acid, and isododecenylsuccinic acid. Carboxylic acids include trivalent or higher carboxylic acids such as 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalentricarboxylic acid, 1,2,4-naphthalentricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empol trimeric acid. These divalent or trivalent or higher carboxylic acid components may be used as ester-forming derivatives such as acid halides, acid anhydrides, and lower alkyl esters. Here, "lower alkyl" means an alkyl group having 1 to 6 carbon atoms.

[0030] When the binder resin is a polyester resin, the softening point of the polyester resin is preferably 70°C to 130°C, and more preferably 80°C to 120°C. To improve the strength of the toner matrix particles and the fixation of the toner, the number-average molecular weight (Mn) of the polyester resin is preferably 1000 to 2000. The molecular weight distribution of the polyester resin (ratio of mass-average molecular weight (Mw) to number-average molecular weight (Mn) Mw / Mn) is preferably 9 to 21.

[0031] As the binder resin, a thermoplastic resin is preferable because it has good adhesion to paper. However, thermoplastic resins can be used alone, or crosslinking agents or thermosetting resins can be added to them. By adding crosslinking agents or thermosetting resins and introducing a partially crosslinked structure into the binder resin, the heat resistance, storage properties, and durability of the toner can be improved without reducing the toner's adhesion. When using a thermosetting resin, the amount of crosslinked portion (gel amount) of the binder resin extracted using a Soxhlet extractor is preferably 10% by mass or less, and more preferably 0.1% by mass or more and 10% by mass or less, relative to the mass of the binder resin.

[0032] Epoxy resins and cyanate resins are preferred thermosetting resins that can be used with thermoplastic resins. Specific examples of suitable thermosetting resins include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, cyclic aliphatic type epoxy resins, and cyanate resins. Two or more of these thermosetting resins can be used in combination.

[0033] The glass transition temperature (Tg) of the binder resin is preferably between 40°C and 70°C. If the glass transition temperature is too high, the low-temperature fixability of the toner tends to decrease. If the glass transition temperature is too low, the heat resistance of the toner tends to decrease.

[0034] The glass transition point of a binder resin can be determined from the point of change in the specific heat of the binder resin using a differential scanning calorimeter (DSC). More specifically, the glass transition point of the binder resin can be determined by measuring the endothermic curve of the binder resin using a differential scanning calorimeter (DSC-6200, manufactured by Seiko Instruments Corporation) as the measuring device. A 10 mg sample is placed in an aluminum pan, and an empty aluminum pan is used as a reference. The glass transition point of the binder resin can be determined from the endothermic curve obtained by measuring the binder resin at room temperature and humidity with a temperature range of 25°C to 200°C and a heating rate of 10°C / min.

[0035] The mass-average molecular weight (Mw) of the binder resin is not particularly limited as long as it does not hinder the objectives of the present invention. Typically, the mass-average molecular weight (Mw) of the binder resin is preferably 20,000 to 300,000, and more preferably 30,000 to 2,000,000. The mass-average molecular weight of the binder resin can be determined by gel permeation chromatography (GPC) using a calibration curve prepared in advance using standard polystyrene resin.

[0036] (magnetic powder) The toner matrix particles contain magnetic powder in the binder resin. Examples of magnetic powder materials include magnetic iron oxides such as magnetite, maghemite, and ferrite, or compounds of divalent metals and iron oxides, powders of metals such as iron, cobalt, and nickel, or alloys of these metals such as aluminum, cobalt, copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures of these powders.

[0037] The particle size of the magnetic powder is not limited as long as it does not hinder the objective of the present invention. Specifically, the particle size of the magnetic powder is preferably 0.05 to 2.0 μm, and more preferably 0.1 μm or more and 1.0 μm or less. When using magnetic powder with such particle size, it is easy to uniformly disperse the magnetic powder in the binder resin.

[0038] Magnetic powders can be surface-treated using surface treatment agents such as titanium-based coupling agents or silane-based coupling agents, for purposes such as improving the dispersibility of magnetic powders in the binder resin.

[0039] The amount of magnetic powder used is not particularly limited as long as it does not hinder the objective of the present invention. Specifically, the amount of magnetic powder used is preferably about 10 to 150 parts by weight, and more preferably 30 to 60 parts by weight, per 100 parts by weight of binder resin. If the amount of magnetic powder is excessive, it may become difficult to form an image with the desired image density over a long period, or the toner's adhesion to the paper may be severely reduced. If the amount of magnetic powder is insufficient, image fogging may occur more easily, or it may become difficult to form an image with the desired image density over a long period.

[0040] (Release agent) Toner matrix particles may contain a release agent to improve adhesion and offset resistance. The type of release agent that can be added to the toner matrix particles is not particularly limited. Wax is preferred as such a release agent, and examples of waxes include carnauba wax, synthetic ester wax, polyethylene wax, polypropylene wax, fluororesin wax, Fischer-Tropsch wax, paraffin wax, montan wax, and rice wax. Two or more of these release agents can be used in combination. By adding such release agents to the toner matrix particles, the occurrence of offset and image smearing (smudges around the image when the image is rubbed) can be suppressed more efficiently.

[0041] When polyester resin is used as the binder resin, from the viewpoint of compatibility, one or more release agents selected from the group consisting of carnauba wax, synthetic ester wax, and polyethylene wax are preferably used as the release agent. Similarly, when polystyrene resin is used as the binder resin, from the viewpoint of compatibility, Fischer-Tropsch wax and / or paraffin wax are preferably used as the release agent.

[0042] Fischer-Tropsch wax is a straight-chain hydrocarbon compound with few iso-structure molecules or side chains, produced using the Fischer-Tropsch reaction, which is a catalytic hydrogenation reaction of carbon monoxide.

[0043] Among Fischer-Tropsch waxes, those with a mass-average molecular weight of 1,000 or more and whose endothermic peak bottom temperature observed by DSC measurement is in the range of 100°C to 120°C are more preferable. Examples of such Fischer-Tropsch waxes include Sazol wax C1 (endothermic peak bottom temperature: 106.5°C), Sazol wax C105 (endothermic peak bottom temperature: 102.1°C), and Sazol wax SPRAY (endothermic peak bottom temperature: 102.1°C), all available from Sazol.

[0044] The amount of release agent used is not particularly limited as long as it does not hinder the objectives of the present invention. Preferably, the amount of release agent used is 1% by mass or more and 10% by mass or less, relative to the total mass of toner matrix particles. If the amount of release agent used is too little, the desired effect of suppressing offset and image smearing in the formed image may not be obtained, and if the amount of release agent used is too much, the heat resistance of the toner may decrease due to fusion of toners.

[0045] (Coloring agent) Since toner matrix particles contain magnetic powder as an essential component, they are usually black. Therefore, the toner may contain known dyes or pigments as colorants for the purpose of adjusting the formed image formed using the toner of the present invention to a more preferred black hue, to the extent that it does not hinder the objectives of the present invention. Specifically, carbon black is an example of a pigment, and acid violet is an example of a dye.

[0046] The amount of colorant used is not particularly limited as long as it does not hinder the objective of the present invention. Specifically, the amount of colorant used is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 7% by mass or less, relative to the total mass of toner matrix particles.

[0047] Furthermore, a colorant can also be used as a masterbatch in which the colorant is pre-dispersed in a resin material such as a thermoplastic resin. When using a colorant as a masterbatch, it is preferable that the resin contained in the masterbatch is the same type of resin as the binder resin.

[0048] (Charge control agent) The toner matrix particles may contain a charge control agent to improve the charge level of the toner and the charge rise characteristics, which are indicators of whether or not it can be charged to a predetermined charge level in a short time, and in order to obtain a toner with excellent durability and stability. Since the toner of the present invention is a positively charged toner, a positively charged charge control agent is used.

[0049] The types of charge control agents that can be contained in the toner matrix particles are not particularly limited as long as they do not hinder the objectives of the present invention, and can be appropriately selected from charge control agents conventionally used in toners. Specific examples of positively charged charge control agents include pyridazine, pyrimidine, pyrazine, orthoxazine, metaoxazine, paraoxazine, orthothiaidine, metathiaidine, parathiaidine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxadiazine2,4,6-oxadiazine, 1,2,3,4-thiadiazine, 1,2,4,6-oxadiazine, 1,2,3,4-tetrazine, 1,2,4,6-oxadiazine, 1,2,3,4-tetrazine, 1,2,4,6-oxadiazine, 1,2,3,4-tetrazine, 1,2,4,6-oxadiazine, 1,2,3,4-tetrazine, 1,2,4 Examples include direct dyes consisting of azine compounds such as din, 1,3,4,5-oxatriazine, phthalazine, quinazoline, and quinoxaline; nigrosine compounds such as nigrosine, nigrosine salts, and nigrosine derivatives; acid dyes consisting of nigrosine compounds such as nigrosine BK, nigrosine NB, and nigrosine Z; metal salts of naphthenic acid or higher fatty acids; triphenylmethane-based dyes; alkoxylated amines; alkylamides; and quaternary ammonium salts such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride. Among these positively charged charge control agents, nigrosine compounds are particularly preferred because they provide a faster charge onset. Two or more of these positively charged charge control agents can be used in combination.

[0050] Resins having quaternary ammonium salts, carboxylates, or carboxyl groups as functional groups can also be used as positively charged charge control agents. More specifically, examples include styrene resins having quaternary ammonium salts, acrylic resins having quaternary ammonium salts, styrene-acrylic resins having quaternary ammonium salts, polyester resins having quaternary ammonium salts, styrene resins having carboxylates, acrylic resins having carboxylates, styrene-acrylic resins having carboxylates, polyester resins having carboxylates, styrene resins having carboxyl groups, acrylic resins having carboxyl groups, styrene-acrylic resins having carboxyl groups, and polyester resins having carboxyl groups. The molecular weight of these resins is not particularly limited as long as it does not hinder the objectives of the present invention, and they may be oligomers or polymers.

[0051] Among resins that can be used as positively charged charge control agents, styrene-acrylic resins having quaternary ammonium salts as functional groups are more preferred because the amount of charge can be easily adjusted to a value within a desired range. Specific examples of preferred acrylic comonomers copolymerized with styrene units in styrene-acrylic resins having quaternary ammonium salts as functional groups include alkyl (meth)acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate.

[0052] Furthermore, as quaternary ammonium salts, dialkylaminoalkyl(meth)acrylates, dialkyl(meth)acrylamides, or units derived from dialkylaminoalkyl(meth)acrylamides through a quaternization process can be used. Specific examples of dialkylaminoalkyl(meth)acrylates include dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate, dipropylaminoethyl(meth)acrylate, and dibutylaminoethyl(meth)acrylate. Specific examples of dialkyl(meth)acrylamides include dimethylmethacrylamide, and specific examples of dialkylaminoalkyl(meth)acrylamides include dimethylaminopropylmethacrylamide. In addition, hydroxyl group-containing polymerizable monomers such as hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, and N-methylol(meth)acrylamide can be used in combination during polymerization.

[0053] The toner matrix particles may be toner matrix particles without a shell layer (non-capsulated toner matrix particles) or toner matrix particles with a shell layer (capsulated toner matrix particles). Capsulated toner matrix particles can be manufactured by forming a shell layer on the surface of non-capsulated toner matrix particles (toner core particles). The shell layer may consist substantially of thermosetting resin only, substantially of thermoplastic resin only, or may contain both thermoplastic resin and thermosetting resin.

[0054] (External additive) The toner of the present invention has its toner matrix particles treated with an external additive. The toner of the present invention contains wet silica particles and metal fine particles as external additives.

[0055] (Wet-processed silica particles) Wet silica particles are produced using methods such as the wet synthesis of silica nanoparticles by hydrolysis of alkoxysilanes, or by methods such as the precipitation method or sol-gel method, which yield silica nanoparticles from sodium silicate in a wet manner.

[0056] The wet silica particles used in the toner of the present invention are surface-treated (coated) with a hydrophobic treatment agent consisting of a long-chain fatty acid ester having at least 18 carbon atoms. Examples of hydrophobic treatment agents consisting of long-chain fatty acid esters include titanate-based coupling agents such as isopropyltriisostearoyl titanate.

[0057] Furthermore, the positive charge properties of toner can be improved by introducing positively charged polar groups to the surface of wet silica particles. A suitable method for introducing positively charged polar groups to wet silica particles is to treat the surface of the wet silica particles with a positively charged surface treatment agent having positively charged polar groups. Examples of positively charged surface treatment agents include silane coupling agents having positively charged polar groups such as amino groups.

[0058] The average particle size of the wet silica particles is preferably between 10 nm and 150 nm. The amount of wet silica particles added is preferably between 0.2% and 0.4% by mass, and more preferably between 0.2% and 0.3% by mass, relative to the mass of the toner matrix particles. By setting the amount of wet silica particles added within the above range, it becomes particularly easier to suppress the occurrence of image fogging when the toner is subjected to mechanical stress in the developer. In addition, it becomes easier to obtain toner with a fluidity change rate of 5% or less.

[0059] The volume resistivity of the wet silica particles used in the toner of the present invention is 10E+7 [Ω·cm] or more and 10E+10 [Ω·cm] or less. If the volume resistivity of the wet silica is too low, the amount of toner charge decreases, making it difficult for the toner to respond to the electric field, thus reducing image density. On the other hand, if the volume resistivity of the wet silica is too high, the amount of toner charge increases, increasing the electrostatic adhesion force, making it difficult for the toner to develop, thus reducing image density. The primary particle diameter of the wet silica particles is preferably 10 nm or more and 100 nm or less. The amount of wet silica particles added is preferably 0.1 to 0.3% by mass relative to the total mass of the toner particles (toner matrix particles and external additives).

[0060] (Conductive inorganic particles) As conductive inorganic particles used in the toner of the present invention, metal oxide particles can be used. Specific examples of metal oxides include alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, barium titanate, antimony trioxide (ATO), and indium tin oxide (ITO). In particular, it is preferable to use one or more selected from alumina, titanium oxide, strontium titanate, and barium titanate.

[0061] The conductive inorganic particles used in the toner of the present invention are surface-modified (hydrophobic treated) with a hydrophobic treatment agent. By hydrophobicizing the surface of the conductive inorganic particles, the surface electrical resistance of the toner particles can be increased, thereby suppressing the leakage of charge from the charged toner.

[0062] Examples of hydrophobic treatment agents for conductive inorganic particles include silicon-containing organic compounds such as silane coupling agents (alkoxysilane compounds, silazane compounds, silicone oils, etc.), titanate-based coupling agents such as isopropyltriisostearoyl titanate, organofluorine compounds, and organic fatty acids.

[0063] The volume resistivity of the conductive inorganic particles used in the toner of the present invention is preferably 1.0E+3 [Ω·cm] or less. The primary particle diameter of the conductive inorganic particles is preferably 200 nm or more and 400 nm or less. The amount of conductive inorganic particles added is preferably 1.0 to 1.5% by mass relative to the total mass of the toner particles (toner matrix particles and external additives).

[0064] In addition to the wet silica particles and conductive inorganic particles described above, other external additives may be added as long as they do not hinder the objectives of the present invention. The types of external additives that can be added are not particularly limited and can be appropriately selected from external additives conventionally used for toners. Specific examples of suitable external additives include silica particles whose surfaces have not been hydrophobicized, and resin particles.

[0065] [4. Toner manufacturing method] Next, the method for manufacturing the toner of the present invention will be described. The method for manufacturing the toner includes a method for manufacturing toner matrix particles and an external additive treatment method for attaching an external additive to the surface of the toner matrix particles. The method for manufacturing the toner matrix particles is not particularly limited as long as the toner matrix particles are formed to have a predetermined structure. In addition, toner matrix particles coated with a shell layer may be used as needed. As a preferred method for manufacturing the positively charged toner described above, the method for manufacturing the toner matrix particles and the external additive treatment method will be described in order below.

[0066] (Method for manufacturing toner matrix particles) The method for producing toner matrix particles is not particularly limited, as long as the magnetic powder and any components such as release agents, colorants, and charge control agents can be well dispersed in the binder resin. Suitable methods for producing toner matrix particles include, for example, grinding or agglomeration.

[0067] The pulverization method involves mixing the binder resin with components such as magnetic powder, colorants, release agents, and charge control agents using a mixer, then melt-kneading the binder resin and the components to be incorporated into the binder resin using a kneader such as a single-screw or twin-screw extruder, and finally pulverizing and classifying the cooled kneaded material. The average particle size of the toner mother particles is not particularly limited as long as it does not hinder the objectives of the present invention, but is generally preferably 5 μm to 10 μm.

[0068] The agglutination method involves agglutinating fine particles of various components, such as a binder resin, magnetic powder, colorant, release agent, and charge control agent, in an aqueous medium until the particles reach a desired size. This forms agglutinated particles containing the binder resin, release agent, charge control agent, and colorant. Subsequently, the resulting agglutinated particles are heated to unify the components contained within them. This yields toner matrix particles with the desired particle size.

[0069] (External processing method) The method for treating toner matrix particles with external additives is not particularly limited, and the toner matrix particles can be treated according to conventionally known methods. Specifically, the treatment conditions are adjusted so that the particles of the external additive do not become embedded in the toner matrix particles, and the toner matrix particles are treated with external additives using a mixer such as a Turbuler mixer, Henschel mixer, Nauter mixer, or V-type mixer.

[0070] The toner of the present invention, as described above, can stabilize the charge amount of the toner when forming images over a long period of time under various environmental conditions such as high temperature and high humidity environments, and low temperature and low humidity environments, thereby enabling the formation of images of the desired density. Furthermore, it can effectively suppress the occurrence of image fogging after durable printing. For this reason, the toner of the present invention can be suitably used in various image forming apparatuses. In particular, it is preferable to use it in an image forming apparatus 100, such as the one shown in Figure 1, which uses a magnetic jumping development method in which the regulating blade 4b is not in contact with the developing roller 4a, and has a process linear velocity of 330 mm / sec or higher, because the charge amount distribution of the toner can be maintained within a desired range, thereby suppressing a decrease in developability. The effects of the present invention will be described in more detail below with reference to examples. However, the present invention is not limited in any way by the examples. [Examples]

[0071] [Manufacturing Example 1] (Manufacturing of toner matrix particles) A mixture was obtained by mixing 100 parts by mass of polyester resin (HP-313, manufactured by Nippon Synthetic Chemical Co., Ltd.) as a binder resin, 4 parts by mass of charge control agent (FCA-201-PS, manufactured by Fujikura Chemical Co., Ltd.), 4 parts by mass of carnauba wax (manufactured by Toa Chemical Co., Ltd.) as a release agent, and 80 parts by mass of magnetic powder (TN-15, manufactured by Mitsui Mining Co., Ltd.) using a Henschel mixer (FM-10 type, manufactured by Mitsui Mining Co., Ltd.).

[0072] The obtained mixture was melt-kneaded using a twin-screw extruder (TEM-26SS, manufactured by Toshiba Machine Co., Ltd.) to obtain a kneaded product. After cooling the kneaded product, it was coarsely ground using a pulverizer (Rotoplex, manufactured by Toa Machinery Co., Ltd.). The obtained coarsely ground product was ground using an air-jet pulverizer (Turbo Mill RS type, manufactured by Turbo Kogyo Co., Ltd.) to obtain finely ground product. The finely ground product was classified using an air-powered classifier (EJ-L-3 (LABO) type, manufactured by Nippon Steel Mining Co., Ltd.) to obtain toner matrix particles with a volume-average primary particle diameter of 7.0 μm.

[0073] [Manufacturing Example 2] (Wet-process silica particle manufacturing) In a 2L stainless steel jacketed reaction vessel equipped with a stirrer, two dropping nozzles, a thermometer, and a circulation pump, an aqueous solution of sodium silicate No. 3 (SiO2 concentration 25% by mass, SiO2 / Na2O molar ratio 3.3) and a 40% by mass aqueous sulfuric acid solution were mixed to obtain a silica hydrosol by reducing the excess sulfuric acid to 0.6N. After allowing the silica hydrosol to gel for a period of time, it was subjected to hydrothermal treatment at 90°C and pH 9.5 for 12 hours. To remove the alkali, sulfuric acid was added until the excess sulfuric acid reached 0.03N, and the mixture was then left at 60°C for 1 hour. After that, it was thoroughly washed with water to obtain a pure silica hydrogel. This silica hydrogel was dried in a dryer until the moisture content was 10%, then pulverized using a superheated steam jet mill (MJT-1, manufactured by Hosokawa Micron Corporation), and further classified using an air classifier (EJ-L-3 (LABO) type, manufactured by Nippon Steel Mining Co., Ltd.) to obtain wet silica particles. The volume resistivity of the wet silica particles was 2.3E+6Ω·cm.

[0074] To 100 parts by mass of the obtained wet silica particles, a solution of 15 parts by mass of isopropyltriisostearoyl titanate (KR-TTS, manufactured by Ajinomoto Co., Inc.) dissolved in 40 parts by mass of toluene was added to form a slurry. The mixed slurry was mixed in a ball mill for 2 hours and then dried to obtain wet silica particles with a hydrophobic surface. The volume resistivity of the wet silica particles after hydrophobic treatment was 4.0E+8Ω·cm.

[0075] [Manufacturing Example 3] (Manufacturing of aluminum oxide particles) 100 parts by mass of aluminum oxide (AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) was dispersed in 1000 parts by mass of water to form a slurry, which was heated to 70°C. To this slurry, an aqueous solution of 10.5 parts by mass of tin chloride pentahydrate dissolved in 100 parts by mass of 2N hydrochloric acid and 6.7N aqueous ammonia were simultaneously added dropwise over approximately 40 minutes to maintain the slurry's pH at 7-8. Subsequently, a solution of 34.4 parts by mass of antimony chloride and 5.3 parts by mass of tin chloride pentahydrate dissolved in 450 parts by mass of 2N hydrochloric acid and 6.7N aqueous ammonia were simultaneously added dropwise over approximately 1 hour to maintain the slurry's pH at 7-8. The slurry was then filtered, washed, and dried at 110°C. Furthermore, it was heat-treated at 500°C in a nitrogen gas stream of 1 L / min for 1 hour to obtain aluminum oxide particles (conductive inorganic fine particles). The volume resistivity of the aluminum oxide particles was 1.22 Ω·cm.

[0076] To 50 parts by mass of the obtained aluminum oxide particles, a solution of 2.5 parts by mass of isopropyltriisostearoyl titanate (KR-TTS, manufactured by Ajinomoto Co., Inc.) dissolved in 40 parts by mass of toluene was added to form a slurry. The mixed slurry was mixed in a ball mill for 2 hours and then dried to obtain aluminum oxide particles with a hydrophobic surface.

[0077] (Manufacturing of titanium dioxide particles) Titanium oxide particles (conductive inorganic fine particles) with a hydrophobic surface treatment were obtained using the same method as for aluminum oxide particles, except that 100 parts by mass of titanium oxide (JR, manufactured by Teika Co., Ltd.) were used instead of 100 parts by mass of aluminum oxide. The volume resistivity of the titanium oxide particles was 55 Ω·cm.

[0078] (Manufacturing of strontium titanate particles) Strontium titanate particles (conductive inorganic fine particles) with a hydrophobic surface treatment were obtained using the same method as for aluminum oxide particles, except that 100 parts by mass of strontium titanate (SW-100, manufactured by Titanium Industry Co., Ltd.) were used instead of 100 parts by mass of aluminum oxide. The volume resistivity of the strontium titanate particles was 88 Ω·cm.

[0079] (Manufacturing of barium titanate particles) Barium titanate particles (conductive inorganic fine particles) with a hydrophobicly treated surface were obtained using the same method as for aluminum oxide particles, except that 100 parts by mass of barium titanate (BT-S, manufactured by Kyoritsu Material Co., Ltd.) were used instead of 100 parts by mass of aluminum oxide. The volume resistivity of the barium titanate particles was 72 Ω·cm.

[0080] [Manufacturing Example 4] (Toner manufacturing) To the toner matrix particles obtained in Production Example 1, 0.7% by mass of silica particles (RA200H, manufactured by Nippon Aerosil Co., Ltd.) whose surface has not been hydrophobized, 0.3% by mass of wet silica particles obtained in Production Example 2, and 1% by mass of aluminum oxide particles obtained in Production Example 3 were added as external additives. The mixture was then mixed for 15 minutes using a Henschel mixer (FM-10 type, manufactured by Mitsui Mining Co., Ltd.) to adhere (add) the silica particles, wet silica particles, and conductive inorganic particles to the toner matrix particles. Subsequently, the mixture was sieved using a vibrating electric sieve (ANF-30, manufactured by Nittokagaku Co., Ltd.) at a mesh size of 200 (mesh opening 75 μm) to obtain toner T-1.

[0081] Toners T-2 to T-6 were obtained using the same method as toner T1, except that the silica particles with untreated surfaces (untreated silica particles), the amount of wet silica particles added, and the type and amount of conductive inorganic particles were changed. Table 1 shows the types and amounts of silica particles and conductive inorganic particles added for toners T-1 to T-6.

[0082] [Table 1]

[0083] (Measurement of nitrogen content in toner) The amount of nitrogen in the toner was measured using a CHN analyzer (2400II, PerkinElmer). The electric furnace temperature was 800°C for the pyrolysis section and 900°C for the catalyst section. The measurement conditions were 300 mL / min main O2 flow rate, 300 mL / min O2 flow rate, and 400 mL / min air flow rate. Quantitative analysis was performed based on a calibration curve created using standard samples such as indomethacin.

[0084] [Evaluation of image color density and image haze] The image density and image fogging were evaluated using toners T-1 to T-4 of Invention 1 to 4 and toners T-5 and T-6 of Comparative Examples 1 and 2 according to the method described below. (Image density) A monochrome printer (ECOSYS PA6000x, manufactured by Kyocera Document Solutions Corporation) was used as the evaluation machine. The toners of Invention 1-4 and Comparative Examples 1 and 2, obtained in Manufacturing Example 4, were installed in the developer unit of the evaluation machine. In addition, replenishment toner (the same toner as that installed in the developer unit) was installed in the toner container of the evaluation machine.

[0085] After toner installation, 100,000 images with 5% coverage were continuously printed in a normal temperature and humidity environment (temperature 23°C, humidity 50%RH). An evaluation image including a solid image was printed on a single sheet of paper at the start of printing (initial) and after 100,000 continuous prints (endurance test).

[0086] The image density (ID) of the evaluation images was measured using a reflectance densitometer (RD914, manufactured by Greda Macbeth). The evaluation criteria for image density are shown below. ○: ID≧1.3 △: 1.2 ≤ ID < 1.3 ×;ID<1.2

[0087] (Image overlap) The fog density (FD) of the white areas (non-image areas) of the evaluation image was measured using a reflectance densitometer (RD914, manufactured by Greda Macbeth). The evaluation criteria for image overexposure are as follows. ○: FD≦0.003 △:0.003 <FD≦0.007 ×: FD>0.007

[0088] Table 2 shows the evaluation results of image density and image fogging when using toners T-1 to T-4 of Invention 1 to 4, and toners T-5 and T-6 of Comparative Examples 1 and 2.

[0089] [Table 2]

[0090] As is clear from Table 2, in toners T-1 to T-4 of the present invention, in which dry silica particles, wet silica particles treated with a hydrophobic treatment agent consisting of long-chain fatty acid esters, and conductive inorganic particles with hydrophobic surfaces were added to the toner base particles, the image density and image fogging evaluations were all good.

[0091] In contrast, in Comparative Example 1, toner T-5, which did not have hydrophobic conductive inorganic particles added to its surface, the image density decreased after 100,000 print runs. Furthermore, slight image fringing occurred after 100,000 print runs.

[0092] Furthermore, in Comparative Example 2, Toner T-6, which did not contain wet silica particles treated with a hydrophobic treatment agent consisting of long-chain fatty acid esters, showed a slight decrease in image density after 100,000 print runs. Significant image fringing also occurred after 100,000 print runs.

[0093] Based on these results, it was confirmed that by adding wet silica particles hydrophobized with a hydrophobic treatment agent consisting of long-chain fatty acid esters, and conductive inorganic particles with a hydrophobic surface treatment, to the toner base particles, a magnetic single-component toner is created that can effectively suppress the decrease in image density and the occurrence of image fogging after durable printing. [Industrial applicability]

[0094] The present invention is applicable to positively charged, single-component magnetic toners used in electrophotographic systems. By utilizing the present invention, it is possible to provide a single-component magnetic toner that improves the blackness of the toner and stabilizes its charge over a long period of time. [Explanation of Symbols]

[0095] 1. Photosensitive drum (image carrier) 4. Developing device 4a Developing roller (toner carrier) 4b Regulatory Blade 6. Transfer roller (transfer device) 100 Image forming apparatus

Claims

1. Toner matrix particles containing at least a binder resin and magnetic powder, The external additive adhering to the surface of the toner matrix particles, A magnetic one-component toner consisting of toner particles containing, The aforementioned external additive is Wet silica particles whose surface is treated with a hydrophobic treatment agent consisting of long-chain fatty acid esters with 18 or more carbon atoms, Conductive inorganic particles whose surfaces have been hydrophobically treated, Includes, A magnetic one-component toner characterized in that the volume resistivity of the wet silica particles is 1.0E+7 [Ω・cm] or more and 1.0E+10 [Ω・cm] or less.

2. The magnetic single-component toner according to claim 1, characterized in that the conductive inorganic particles are one or more selected from aluminum oxide particles, titanium oxide particles, strontium titanate particles, and barium titanate particles.

3. The magnetic one-component toner according to claim 1, characterized in that the hydrophobic treatment agent comprising the long-chain fatty acid ester is isopropyltriisostearoyl titanate, and the amount of isopropyltriisostearoyl titanate added is 5% by mass or more and 20% by mass or less relative to the wet silica particles.

4. The magnetic one-component toner according to claim 1, further comprising silica particles whose surface has not been hydrophobized as the external additive.

5. A developing apparatus for developing an electrostatic latent image formed on an image carrier into a toner image using a magnetic one-component toner according to any one of claims 1 to 4, A transfer device for transferring the toner image developed by the developing device onto a recording medium, Equipped with, The developing apparatus is a magnetic single-component jumping developing method that charges the magnetic single-component toner via a toner carrier that carries the magnetic single-component toner, An image forming apparatus in which the linear velocity of the image carrier is 330 mm / sec or higher.

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