One-component magnetic toner

Abstract

This invention provides a magnetic single-component toner that can suppress image density reduction and image fogging by stabilizing the toner's electrostatic properties over a long period of time. [Solution] The magnetic single-component toner consists of toner particles comprising toner matrix particles containing at least a binder resin and magnetic powder, and an external additive attached to the surface of the toner matrix particles. The toner matrix particles contain a ferroelectric material made of a metal titanate salt, and the dielectric constant of the toner matrix particles is 8.0 [F / m] or more and 12.0 [F / m] or less.

Description

Technical Field

[0001] The present invention relates to a magnetic one-component toner.

Background Art

[0002] Generally, in the electrophotographic method, after the surface of an 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 onto a recording medium to obtain a high-quality image.

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

[0004] In the magnetic one-component development method, a toner layer is held in the gap between a development sleeve and a regulating blade by magnetic force, and the toner is rubbed against the surface of the development sleeve to charge the toner. Therefore, there is a problem that the mechanical stress applied to the toner is large, and the external additives are buried or detached during durable printing, resulting in image defects such as a decrease in image density and image fogging.

[0005] Therefore, various methods for stabilizing the chargeability of toner have been proposed to solve the above problems. Patent Document 1 discloses an electrophotographic toner in which a ferroelectric substance is added internally in an amount of 10 to 70 parts by weight or externally in an amount of 10 to 30 parts by weight to the toner. Patent Document 2 discloses a toner containing toner particles having at least a binder resin and a colorant, and an inorganic fine powder having a perovskite-type crystal with a number average particle diameter Ds (nm) of primary particles of 30 nm or more and 300 nm or less and a particle shape of cubic and / or rectangular parallelepiped shapes, and a composite particle in which carbon black is coated on core particles α as conductive particles on the surface layer of a charging member and satisfies Ds / 20≦Dc≦Ds in terms of the number average particle diameter Dc (nm).

[0006] Patent Document 3 discloses a magnetic toner comprising toner matrix particles and an external additive attached to the surface of the toner matrix particles, wherein the toner matrix particles include a binder resin, magnetic powder, and strontium titanate particles, the magnetic powder includes magnetite particles as magnetic particles, and the number-average primary particle diameter of the strontium titanate particles is 350 nm or less. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 5-224454 [Patent Document 2] Japanese Patent Publication No. 2007-206470 [Patent Document 3] Japanese Patent Publication No. 2020-86226 [Overview of the project] [Problems that the invention aims to solve]

[0008] Patent Document 1 describes designing the dielectric constant of toner by adding a ferroelectric material to the toner core particles, but the toner in Patent Document 1 is a non-magnetic toner that does not contain magnetic powder. Therefore, it could not be applied to a magnetic single-component development method.

[0009] Furthermore, while Patent Document 2 employs inorganic fine powder of a ferroelectric material as an external additive, the mechanical stress applied during durable printing causes the external additive to become embedded in or detach from the toner particles, making it difficult to stabilize the toner's charge over a long period. In Patent Document 3, strontium titanate is internally added to the toner matrix particles, but since the toner dielectric constant is not specified, there was a risk that the desired toner charge could not be secured.

[0010] In view of the above problems, the present invention aims to provide a magnetic single-component toner that can suppress the decrease in image density and the occurrence of image fogging by stabilizing the toner's chargeability over a long period of time. [Means for solving the problem]

[0011] To achieve the above objective, the first configuration of the present invention is a magnetic one-component toner comprising toner particles comprising toner matrix particles containing at least a binder resin and magnetic powder, and an external additive attached to the surface of the toner matrix particles. The toner matrix particles contain a ferroelectric material made of a metal titanate salt, and the dielectric constant of the toner matrix particles is 8.0 [F / m] or more and 12.0 [F / m] or less. [Effects of the Invention]

[0012] According to the first configuration of the present invention, by stabilizing the toner's chargeability over a long period of time, a magnetic single-component toner is obtained that can suppress the decrease in image density and the occurrence of image fogging after durable printing. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described in detail below. Unless otherwise specified, the evaluation results (values ​​indicating shape or physical properties, etc.) for the powder (more specifically, toner core particles, toner mother particles, external additives, or toner, etc.) are the number average 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 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 median volume 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.

[0014] 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".

[0015] 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.

[0016] The toner particles contained in this embodiment comprise toner mother particles and an external additive attached to the surface of the toner mother particles. That is, toner particles before the external additive is attached are referred to as toner mother particles. Furthermore, if the toner mother particles have a shell layer, the particles before the shell layer is formed are referred to as toner core particles. If the toner mother particles do not have a shell layer, the toner mother particles are also referred to as toner core particles.

[0017] The toner according to this embodiment can be used, for example, to form images in an electrophotographic apparatus (image forming apparatus). An example of an image forming method using an electrophotographic apparatus will be described below.

[0018] First, an electrostatic latent image is formed on a photoreceptor (e.g., the surface layer of a photoreceptor drum) based on image data. Next, the formed electrostatic latent image is developed using a magnetic single-component toner. In the developing process, toner (e.g., toner charged by friction with a blade) on a developing sleeve (e.g., the surface layer of a developing roller in a developer) disposed near the photoreceptor is attached to the electrostatic latent image to form a toner image on the photoreceptor. Then, in the subsequent transfer process, the toner image on the photoreceptor is directly transferred to a recording medium (e.g., paper). Alternatively, after primary transfer to an intermediate transfer body (e.g., a transfer belt), the toner image on the intermediate transfer body is further secondarily transferred to the recording medium. Thereafter, the toner is heated to fix the toner to the recording medium. As a result, an image is formed on the recording medium.

[0019] [1. Basic Composition of Toner] The magnetic single-component toner of the present invention (hereinafter, also simply referred to as toner) includes toner mother particles and an external additive attached to the surface of the toner mother particles. The toner mother particles contain at least a binder resin, magnetic powder, and a ferroelectric material. Further, the toner mother particles may contain a colorant, a charge control agent, etc. in the binder resin as necessary.

[0020] The toner of the present invention has a configuration in which a ferroelectric material is contained inside the toner mother particles. The dielectric constant of the toner mother particles is adjusted to 8.0 [F / m] or more and 12.0 [F / m] or less by the ferroelectric material.

[0021] [2. Materials of Toner] Hereinafter, the binder resin, magnetic powder, ferroelectric material, release agent, colorant, charge control agent for forming the toner mother particles, and the external additive externally added to the toner mother particles, and the manufacturing method of the toner of the present invention will be described in order.

[0022] (Binder Resin) The toner mother particles constituting the toner of the present invention contain a binder resin. The binder resin that can be contained in the toner mother particles is not particularly limited as long as it is a resin conventionally used as a binder resin for toner. Specific examples of the binder resin 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 a polyester resin and a styrene-acrylic acid resin, and a polyester resin is more preferable, from the viewpoints of the dispersibility of the colorant in the binder resin, the charging property of the toner, and the fixing property to the paper. Hereinafter, the polyester resin will be described.

[0023] As the polyester resin, those obtained by polycondensation or co-polycondensation of a dihydric or trihydric or higher alcohol component and a dihydric or trihydric or higher carboxylic acid component can be used. Examples of the components used when synthesizing the polyester resin include the following alcohol components and carboxylic acid components.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] (magnetic powder) The toner matrix contains magnetic powder in the binder resin. Suitable materials for the magnetic powder include, for example, ferromagnetic metals (more specifically, iron, cobalt, nickel, or alloys containing one or more of these metals), ferromagnetic metal oxides (more specifically, ferrite, magnetite, or chromium dioxide), or materials that have undergone ferromagnetic treatment (more specifically, carbon materials to which ferromagnetism has been imparted by heat treatment). To suppress the elution of metal ions (e.g., iron ions) from the magnetic powder, it is preferable to use surface-treated magnetic particles as the magnetic powder. One type of magnetic powder may be used alone, or multiple types of magnetic powder may be used in combination.

[0033] 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 0.1 μm or more and 1.0 μm or less, and more preferably 0.1 μm or more and 0.5 μm or less. When magnetic powder with such particle size is used, it is easy to uniformly disperse the magnetic powder in the binder resin.

[0034] 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.

[0035] 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 30% to 60% by mass, and more preferably 40% to 60% by mass, relative to the total mass of toner. If the amount of magnetic powder used is excessive, it may become difficult to form an image with the desired image density over a long period of time, or the toner's adhesion to the paper may be severely reduced. If the amount of magnetic powder used is insufficient, the formed image may be prone to blurring, or it may become difficult to form an image with the desired image density over a long period of time.

[0036] (Ferroelectric materials) The toner matrix particles contain a ferroelectric material in the binder resin. Metal titanate salts are used as the ferroelectric material. Specific examples of metal titanate salts include strontium titanate, magnesium titanate, calcium titanate, and barium titanate. Two or more ferroelectric materials can also be used in combination.

[0037] The dielectric constant of the toner matrix particles can be adjusted by changing the amount of ferroelectric material added. In the toner of this invention, the dielectric constant of the toner matrix particles is adjusted to be between 8.0 [F / m] and 12.0 [F / m]. If the dielectric constant of the toner matrix particles is less than 8.0 [F / m], the toner's chargeability becomes too high, making image fringing more likely. Furthermore, the unstable toner chargeability leads to a decrease in image density after durable printing. On the other hand, if the dielectric constant of the toner matrix particles exceeds 12.0 [F / m], the toner's chargeability becomes too low, making a decrease in image density more likely.

[0038] (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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] (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.

[0044] 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.

[0045] 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.

[0046] (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.

[0047] 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 azine compounds such as 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-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline, and quinoxaline; azine compounds Examples include direct dyes consisting of azine compounds such as Stread FC, Azin Fast Red 12BK, Azin Violet BO, Azin Brown 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Deep Black EW, and Azin Deep Black 3RL; 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; 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 rise. Two or more of these positively charged charge control agents can be used in combination.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The amount of charge control agent used is not particularly limited as long as it does not hinder the objectives of the present invention. Typically, the amount of charge control agent used is preferably 0.1% by mass or more and 10% by mass or less, relative to the total mass of toner matrix particles. If the amount of charge control agent used is insufficient, it is difficult to stably charge the toner to a predetermined polarity, which may result in the image density of the formed image falling below the desired value or making it difficult to maintain the image density over a long period of time. In addition, because the charge control agent is difficult to disperse uniformly, the formed image is more prone to blurring, and contamination of the latent image-carrying area by toner components is more likely to occur. If the amount of charge control agent used is excessive, the environmental resistance deteriorates, making it easier for image defects in the formed image due to poor charging under high temperature and high humidity conditions, and contamination of the latent image-carrying area by toner components to occur.

[0052] 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.

[0053] (External additive) The toner of the present invention has its toner matrix particles treated with an external additive. The type of external additive is not particularly limited as long as it does not hinder the objective of the present invention, and can be appropriately selected from external additives conventionally used for toner. Specific examples of suitable external additives include silica, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, barium titanate and other metal oxides, and resin particles. Two or more of these external additives can be used in combination.

[0054] The particle size of the external additive is not particularly limited as long as it does not hinder the objective of the present invention, but is typically preferably 0.01 μm or more and 1.0 μm or less.

[0055] The amount of external additive used is not particularly limited as long as it does not hinder the objectives of the present invention. Typically, the amount of external additive used is preferably 0.1% to 10% by mass, and more preferably 0.2% to 5% by mass, relative to the total mass of toner matrix particles manufactured by forming a shell layer on the surface of toner core particles. If the amount of external additive used is insufficient, the hydrophobicity of the toner tends to decrease. As a result, it becomes more susceptible to the influence of water molecules in the air under high temperature and high humidity environments, and problems such as a decrease in image density of the formed image due to an extreme decrease in the charge amount of the toner, and a decrease in toner fluidity are likely to occur. On the other hand, if the amount of external additive used is excessive, there is a risk of a decrease in image density due to excessive toner charge buildup.

[0056] [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.

[0057] (Method for manufacturing toner matrix particles) The method for producing toner matrix particles is not particularly limited, as long as magnetic powder and any components such as colorants, release agents, 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.

[0058] 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.

[0059] 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.

[0060] (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 the external additive using a mixer such as a Henschel mixer or a Nauter mixer.

[0061] 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. 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 these examples. [Examples]

[0062] [Manufacturing Example 1] (Production of strontium titanate) A hydrated titanium oxide slurry, which had undergone desulfurization and gelatinization treatment, was added to a 2L stainless steel jacketed reaction vessel equipped with a stirrer, two dropping nozzles, a thermometer, and a circulation pump. The added hydrated titanium oxide slurry contained 0.626 mol of titanium oxide (TiO2). Next, an aqueous strontium chloride solution was added to the reaction vessel in an amount such that the molar ratio of strontium oxide (SrO) to titanium oxide in the reaction vessel (SrO / TiO2) was 1.15.

[0063] Next, deionized water was added to the reaction vessel to adjust the titanium dioxide concentration in the reaction vessel to 0.626 mol / L. Then, nitrogen gas was blown into the reaction vessel and left for 20 minutes to replace the contents with nitrogen gas. Next, with nitrogen gas flowing through the reaction vessel, the solution containing metatitanic acid and strontium chloride was heated to 90°C at a rate of 13.5°C / min while stirring at a rotation speed of 300 rpm.

[0064] Subsequently, while maintaining the mixed solution at 90°C, 143 mL of 2.5N sodium hydroxide aqueous solution was added to the reaction vessel over 12 hours while stirring at a rotation speed of 300 rpm. Then, under a nitrogen atmosphere, the contents were reacted by stirring at a rotation speed of 300 rpm for 1 hour at 90°C.

[0065] After the reaction, the internal temperature of the reaction vessel was cooled to 40°C. Next, the supernatant liquid of the contents of the reaction vessel was removed under a nitrogen atmosphere. Then, under a nitrogen atmosphere, the contents were washed by adding 2.5 L of pure water to the reaction vessel and removing the supernatant liquid by decantation, repeating this procedure twice.

[0066] Next, the contents of the reaction vessel were filtered through a Buchner funnel, and the resulting cake-like solid was dried in air at 110°C for 8 hours. This yielded strontium titanate particles with a volume-average primary particle size of 100 nm and a relative permittivity of 135.3.

[0067] [Manufacturing Example 2] (Manufacturing of magnesium titanate) (2-1. Reaction preparation step) Metatitanic acid obtained by the sulfuric acid method was deferred, and then a sodium hydroxide aqueous solution was added to the deferred metatitanic acid to prepare a pH 9.0 suspension. The obtained suspension was desulfurized, and then hydrochloric acid was added to the desulfurized suspension to adjust the pH of the suspension to 5.8. Next, the suspension adjusted to pH 5.8 was filtered (solid-liquid separation), the obtained solids were washed with water, and then deionized water was added to the washed solids to obtain a slurry with a Ti concentration of 2.13 mol / L. The obtained slurry was dispasticated by adding hydrochloric acid. The pH of the slurry after dispastication was 1.4.

[0068] Next, the slurry after disaccharification (1.8770 mol in terms of TiO2) was added to a 3 L reaction vessel. Then, an aqueous solution of magnesium chloride (MgCl2) equivalent to 2.1590 mol of magnesium was added to the reaction vessel. After adding the aqueous magnesium chloride solution, the contents of the reaction vessel (hereinafter simply referred to as "container contents") had a molar ratio of Mg to Ti (Mg / Ti) of 1.15.

[0069] Next, an aqueous solution of lanthanum chloride (LaCl3) was added to the reaction vessel at a concentration of La (0.2160 mol). After adding the lanthanum chloride solution, the molar ratio of La to Mg (La / Mg) in the contents of the vessel was 0.10. Next, niobium pentoxide (Nb2O5) was added to the reaction vessel at a concentration of Nb (0.0188 mol). After adding the niobium pentoxide, the molar ratio of Nb to Ti (Nb / Ti) in the contents of the vessel was 0.01. Then, deionized water was added to the contents of the vessel to obtain a slurry with a Ti concentration of 0.939 mol / L.

[0070] (2-2. Reaction Process) The slurry (Ti concentration: 0.939 mol / L) obtained in the reaction preparation step was stirred, and the internal temperature of the reaction vessel was raised to 90°C. Then, 553 mL of sodium hydroxide aqueous solution (NaOH concentration: 10 mol / L) was added to the reaction vessel at a constant rate over 1 hour. Next, the internal temperature of the reaction vessel was raised to 95°C, and the contents of the vessel were stirred for 1 hour while maintaining the internal temperature at 95°C. Next, the contents of the vessel were cooled to 50°C, and hydrochloric acid was added to the cooled contents to adjust the pH of the contents to 5.0. Next, the contents of the vessel were stirred for 1 hour while maintaining the internal temperature at 50°C to obtain a precipitate. The obtained precipitate was washed by decantation and filtered (solid-liquid separation). The obtained solids were dried in air at 120°C for 10 hours to obtain a magnesium titanate powder containing lanthanum and niobium.

[0071] (2-3. Hydrophobic Treatment Process) 100 parts by mass of magnesium titanate particles obtained in the reaction step were placed in a three-necked flask equipped with a thermometer and a stirring device, and the air inside the flask was replaced with nitrogen to create a nitrogen atmosphere. Subsequently, while stirring the contents of the flask, 15 parts by mass of isobutyltrimethoxysilane and an amount of distilled water suitable for promoting the reaction (specifically, hydrolysis) on the surface of the magnesium titanate particles were sprayed into the flask. Then, while stirring the contents of the flask, the magnesium titanate particles and isobutyltrimethoxysilane were reacted at a temperature of 110°C for 2 hours. As a result, a powder of magnesium titanate particles was obtained in which isobutyl groups (specifically, isobutyl groups derived from isobutyltrimethoxysilane) were introduced to the surface of the magnesium titanate particles (substrate), thereby hydrophobizing the particles.

[0072] [Manufacturing Example 3] (Production of calcium titanate) (3-1. Reaction preparation process) Metatitanic acid obtained by the sulfuric acid method was deferred, and then a sodium hydroxide aqueous solution was added to the deferred metatitanic acid to prepare a pH 9.0 suspension. The obtained suspension was desulfurized, and then hydrochloric acid was added to the desulfurized suspension to adjust the pH of the suspension to 5.8. Next, the suspension adjusted to pH 5.8 was filtered (solid-liquid separation), the obtained solids were washed with water, and then deionized water was added to the washed solids to obtain a slurry with a Ti concentration of 2.13 mol / L. The obtained slurry was dispasticated by adding hydrochloric acid. The pH of the slurry after dispastication was 1.4.

[0073] Next, the slurry after disaccharification (1.8770 mol in terms of TiO2) was added to a 3 L reaction vessel. Then, an aqueous solution of calcium chloride (CaCl2) equivalent to 2.1590 mol in terms of Ca was added to the reaction vessel. After adding the aqueous calcium chloride solution, the molar ratio of Ca to Ti (Ca / Ti) in the contents of the vessel was 1.15.

[0074] Next, an aqueous solution of lanthanum chloride (LaCl3), equivalent to 0.2160 mol of La, was added to the reaction vessel. After adding the lanthanum chloride solution, the molar ratio of La to Ca (La / Ca) in the contents of the vessel was 0.10. Next, 0.0188 mol of niobium pentoxide (Nb2O5), equivalent to 0.0188 mol of Nb, was added to the reaction vessel. After adding the niobium pentoxide, the molar ratio of Nb to Ti (Nb / Ti) in the contents of the vessel was 0.01. Finally, deionized water was added to the contents of the vessel to obtain a slurry with a Ti concentration of 0.939 mol / L.

[0075] (3-2. Reaction Process) The slurry obtained in the reaction preparation step (Ti concentration: 0.939 mol / L) was stirred while the internal temperature of the reaction vessel was raised to 90°C. Then, 553 mL of sodium hydroxide aqueous solution (NaOH concentration: 10 mol / L) was added to the reaction vessel at a constant rate over 1 hour. Next, the internal temperature of the reaction vessel was raised to 95°C, and the contents of the vessel were stirred for 1 hour while maintaining the internal temperature at 95°C. Next, the contents of the vessel were cooled to 50°C, and hydrochloric acid was added to the cooled contents to adjust the pH of the contents to 5.0. Next, the contents of the vessel were stirred for 1 hour while maintaining the internal temperature at 50°C to obtain a precipitate. The obtained precipitate was washed by decantation and filtered (solid-liquid separation). The obtained solids were dried in air at 120°C for 10 hours to obtain a powder of calcium titanate particles containing lanthanum and niobium.

[0076] (3-3. Hydrophobic Treatment Process) 100 parts by mass of calcium titanate particles obtained in the reaction step were placed in a three-necked flask equipped with a thermometer and a stirrer, and the air inside the flask was replaced with nitrogen to create a nitrogen atmosphere. Subsequently, while stirring the contents of the flask, 15 parts by mass of isobutyltrimethoxysilane and an amount of distilled water suitable for promoting the reaction (specifically, hydrolysis) on the surface of the calcium titanate particles were sprayed into the flask. Then, while stirring the contents of the flask, the calcium titanate particles and isobutyltrimethoxysilane were reacted at a temperature of 110°C for 2 hours. As a result, a powder of calcium titanate particles was obtained in which isobutyl groups (specifically, isobutyl groups derived from isobutyltrimethoxysilane) were introduced to the surface of the calcium titanate particles (substrate), thereby hydrophobizing the particles.

[0077] [Manufacturing Example 4] (Manufacturing of toner matrix particles) As a binder resin, 100 parts by mass of polyester resin (HP-313, manufactured by Nippon Synthetic Chemical Co., Ltd.), 80 parts by mass of magnetic powder (TN-15, manufactured by Mitsui Mining & Smelting Co., Ltd.), 4 parts by mass of charge control agent (FCA-201-PS, manufactured by Fujikura Chemical Co., Ltd.), 4 parts by mass of mold release agent (carnauba wax, manufactured by Toa Chemical Co., Ltd.), and 14 parts by mass of strontium titanate particles obtained in Production Example 1 as a ferroelectric material were mixed using an FM mixer (FM-20B, manufactured by Nippon Coke Industries Co., Ltd.) at a rotation speed of 2000 rpm for 5 minutes to obtain a mixture.

[0078] The obtained mixture was melt-kneaded using a twin-screw extruder (TEM-26SS, manufactured by Toshiba Machine Co., Ltd.) to obtain a kneaded product. The melt-kneading was performed under the conditions of a cylinder temperature of 120°C, a shaft rotation speed of 100 rpm, and a processing rate of 90 g / min. After the kneaded product was cooled, it was coarsely ground using a pulverizer (Rotoplex 16 / 8 type, manufactured by Hosokawa Micron Corporation). The obtained coarsely ground product was ground using a mechanical pulverizer (Turbomill TA, manufactured by Freund Turbo) to obtain a pulverized product. The pulverized product was classified using an air classifier (EJ-L-3 (LABo) type, manufactured by Nippon Steel Mining Co., Ltd.) to obtain toner mother particles A with a number mean primary particle diameter of 7.0 μm.

[0079] Toner matrix particles B, C, E, and F were obtained in the same manner as toner matrix particle 1, except that the amount of magnetic powder added was changed to 50 parts by mass and the amount of strontium titanate particles added was changed to a predetermined amount.

[0080] Toner matrix particles D were obtained in the same manner as toner matrix particles A, except that the amount of magnetic powder added was changed to 50 parts by mass, the amount of strontium titanate added to 10 parts by mass, and an additional 1.0 part by mass of barium titanate (HPBT, manufactured by Fuji Titanium Industries Co., Ltd.) was added.

[0081] (Measurement of the dielectric constant of toner matrix particles) 1g of toner matrix particles under a pressure of 200kg / cm² 2 The material was compressed for 2 minutes under the specified conditions to form a disc-shaped pellet (measurement sample) with a diameter of 25 mm and a thickness of 1 mm. Next, the measurement sample was placed in a rotary rheometer (ARES-G2, manufactured by TA Instruments) equipped with a dielectric constant measurement jig (electrode) with a diameter of 25 mm. Then, using an LCR meter (4284A Precision LCR meter, manufactured by Keysight Technologies), the dielectric constant of the toner matrix particles was measured under the conditions of a measurement temperature of 25°C, a load of 150 g, an applied voltage of 1.0 V, and a frequency of 1.0 MHz.

[0082] [Manufacturing Example 5] (Toner manufacturing) Toner matrix particles A to F obtained in Production Example 4, 1% by mass of silica particles (RA200H, manufactured by Nippon Aerosil Co., Ltd.) was added and mixed for 15 minutes using a Henschel mixer (manufactured by Mitsui Miike Industries Co., Ltd.) to adhere (externally add) the silica particles to the toner matrix particles. Subsequently, the mixture was sieved using a 100-mesh sieve (mesh opening 150 μm) to obtain toners for Inventions 1 to 4 and Comparative Examples 1 to 2.

[0083] Table 1 shows the types of ferroelectric materials, amounts added, amounts of magnetic powder added, and dielectric constants of the toner matrix particles contained in the toners of Inventions 1-4 and Comparative Examples 1-2.

[0084] [Table 1]

[0085] [Evaluation of image color density and image haze] The image density and image fogging were evaluated using the toners of Invention 1-4 and Comparative Examples 1-2 according to the method described below. (Image density) The toners of Invention 1-4 and Comparative Examples 1-4, obtained in Manufacturing Example 3, were installed in the developer unit of an evaluation machine (monochrome printer ECOSYS LS-4200DN, manufactured by Kyocera Document Solutions). After toner installation, 100,000 test images with a print density of 5% were printed in a normal temperature and humidity environment (temperature 23°C, humidity 50%RH). Image density (ID) was measured immediately after the start of printing (initial) and after 100,000 prints (endurance) using a reflectance densitometer (RD914, manufactured by Gretag Macbeth). The evaluation criteria for image density are shown below. ○: ID≧1.3 △; 1.2 ≤ ID < 1.3 ×;ID<1.2

[0086] (Image overlap) The fog density (FD) of the white areas of the printed images was measured using a reflectance densitometer (RD914, manufactured by Gretag Macbeth) immediately after the start of printing (initial) and after 100,000 prints (endurance). The fog density (FD) was calculated using the following formula (1). FD = (Reflectance density of the white area of ​​the printed paper) - (Reflectance density of the unprinted paper). The evaluation criteria for image haze are shown below. ○: FD<0.003 △: 0.003 ≤ FD ≤ 0.007 ×: FD>0.007

[0087] Table 2 shows the evaluation results of image density and image fogging when using the toners of Invention 1 to 4 and Comparative Examples 1 to 2.

[0088] [Table 2]

[0089] As is clear from Table 2, in the toners of the present invention 1 to 4, in which the dielectric constant of the toner matrix particles was set to 8.0 [F / m] or more and 12.0 [F / m] or less using a ferroelectric material, the image density (ID) was 1.3 or higher both initially and after printing 100,000 sheets, which was good. Furthermore, the fogging density (FD) after printing 100,000 sheets was less than 0.003, and no image fogging was observed.

[0090] In contrast, the toner in Comparative Example 1, which had a dielectric constant of 7.9 [F / m] for the toner matrix particles, showed an image density (ID) of 1.29 after printing 100,000 pages, indicating a decrease in image density. Furthermore, the fogging density (FD) after printing 100,000 pages was 0.003, indicating that image fogging occurred.

[0091] On the other hand, in Comparative Example 2, where the dielectric constant of the toner matrix particles was 12.1 [F / m], the image density (ID) after printing 100,000 sheets was 1.22, indicating that sufficient image density could not be obtained. Furthermore, in the toner of Comparative Example 2, the fogging density (FD) after printing 100,000 sheets was 0.001, and no image fogging was observed. The reason for this is thought to be that the volume resistivity of strontium titanate is lower than that of other materials (such as binder resins), so an excessive amount of strontium titanate was added, increasing the exposed area on the surface of the toner matrix particles and lowering the surface resistance of the toner, or that the charge of the toner decreased due to the low charge of strontium titanate itself, resulting in a decrease in fogging density.

[0092] Based on these results, it was confirmed that by using a ferroelectric material to set the dielectric constant of the toner matrix particles to between 8.0 [F / m] and 12.0 [F / m], a magnetic single-component toner can be produced that maintains image density after durable printing while suppressing the occurrence of image fogging. [Industrial applicability]

[0093] This invention is applicable to positively charged, single-component magnetic toners used in electrophotographic systems. By utilizing this invention, it is possible to provide a single-component magnetic toner that can stabilize the toner's charge over a long period of time, thereby suppressing image density reduction and image fogging.

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 toner matrix particles include a ferroelectric material made of a metal titanate salt. A magnetic single-component toner characterized in that the dielectric constant of the toner matrix particles is 8.0 [F / m] or more and 12.0 [F / m] or less.

2. The magnetic single-component toner according to claim 1, characterized in that the titanate metal salt is one or more selected from strontium titanate, magnesium titanate, calcium titanate, and barium titanate.

3. The magnetic one-component toner according to claim 1, characterized in that the external additive is silica particles.

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