JP6471723B2 - Magnetic toner - Google Patents

Description

  The present invention relates to an electrostatic latent image developing toner.

  A MICR (Magnetic Ink Character Recognition) system is known as a forgery prevention method using an identification mark. The MICR system uses magnetic ink or magnetic toner to print a predetermined identification mark on a predetermined medium (more specifically, a check, securities, bill, or ticket), and then distributes the medium. Let In general, the identification mark is composed of a combination of numbers and symbols. After distribution, the authenticity of the medium is judged by reading predetermined information (more specifically, the shape of the mark, magnetic information, etc.) included in the identification mark using a dedicated reader. Can do.

  For example, Patent Document 1 discloses a magnetic toner (MICR toner) used in the MICR system. In the magnetic toner described in Patent Document 1, the residual magnetization σr of the toner particles is 4 ≦ σr ≦ 7 emu / g.

JP-A-6-282100

  However, only the technique disclosed in Patent Document 1 is excellent in magnetic powder dispersibility, magnetic readability, and fixability, and forms high-quality images in both normal temperature and high humidity environments. It is difficult to provide a magnetic toner that can be used.

  The present invention has been made in view of the above problems, and is excellent in the dispersibility, magnetic readability, and fixability of magnetic powder, and has high image quality in both normal temperature and high humidity environments. It is an object of the present invention to provide a magnetic toner capable of forming a toner.

  The magnetic toner according to the present invention includes a plurality of toner particles containing a crystalline polyester resin, an amorphous resin, and magnetic powder. The magnetic powder includes acicular magnetic powder that is a powder of acicular magnetic particles having an aspect ratio of 2.0 or more, and non-acicular magnetic powder that is a powder of non-acicular magnetic particles having an aspect ratio of less than 2.0. including. The acicular magnetic particles are surface-treated with nigrosine. The residual magnetization of the magnetic toner is 7 emu / g or more and 20 emu / g or less.

  According to the present invention, there is provided a magnetic toner that is excellent in dispersibility, magnetic readability, and fixability of magnetic powder, and can form a high-quality image in any environment of normal temperature and normal humidity and high temperature and high humidity. Is possible.

  An embodiment of the present invention will be described. It should be noted that the evaluation results (values indicating the shape or physical properties) of the powder (more specifically, toner base particles, magnetic powder, external additive, toner, etc.) are from the powder unless otherwise specified. A considerable number of average particles are selected and the number average of the values measured for each of the average particles.

The number average particle diameter of the powder is the number average value of the equivalent circle diameter of primary particles (diameter of a circle having the same area as the projected area of the particles) measured using a microscope unless otherwise specified. . Moreover, the measured value of the volume median diameter (D ₅₀ ) of the powder is measured using a laser diffraction / scattering particle size distribution measuring device (“LA-750” manufactured by Horiba, Ltd.) unless otherwise specified. It is the value. Moreover, the softening point (Tm) is a value measured using a Koka type flow tester (“CFT-500D” manufactured by Shimadzu Corporation) unless otherwise specified. In the S curve (horizontal axis: temperature, vertical axis: stroke) measured with the Koka type flow tester, the temperature that becomes "(baseline stroke value + maximum stroke value) / 2" is Tm (softening point). Equivalent to. Moreover, the measured value of melting | fusing point (Mp) is the temperature of the maximum endothermic peak in the DSC curve measured using a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.) unless otherwise specified. It is. Moreover, the measured value of a BET specific surface area is the value measured using the fully automatic BET specific surface area measuring apparatus ("Macsorb (registered trademark) HM MODEL-1208" by Mountec Co., Ltd.) unless otherwise specified.

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. When the name of a polymer is expressed by adding “system” after the compound name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof. Acrylic and methacrylic are sometimes collectively referred to as “(meth) acrylic”.

  The magnetic toner according to the present embodiment can be suitably used for developing an electrostatic latent image, for example, as a one-component developer made of a positively chargeable toner in an MICR system. The magnetic toner of the present embodiment is a powder containing a plurality of toner particles (magnetic particles each having a configuration described later).

  The magnetic toner according to this embodiment can be used for image formation in, for example, an electrophotographic apparatus (image forming apparatus). The positively chargeable toner is positively charged by friction in the image forming apparatus. Hereinafter, an example of an image forming method using an electrophotographic apparatus will be described.

  First, an electrostatic latent image is formed on a photoconductor (for example, a surface layer portion of an amorphous silicon (a-Si) photoconductor drum) based on image data. Next, the formed electrostatic latent image is developed using toner. In the developing process, toner (for example, toner charged by friction with a blade) on a developing sleeve (for example, a surface layer of a developing roller in the developing device) disposed in the vicinity of the photosensitive member is attached to the electrostatic latent image. Thus, a toner image is formed on the photoreceptor. In the subsequent transfer process, the toner image on the photoconductor is transferred to a recording medium (for example, paper). Thereafter, the toner is heated to fix the toner on the recording medium. As a result, an image is formed on the recording medium.

  The magnetic toner according to this embodiment includes a plurality of toner particles. The toner particles may include an external additive. When the toner particles include an external additive, the toner particles include a toner base particle and an external additive. The external additive adheres to the surface of the toner base particles. The toner base particles contain a binder resin and magnetic powder. The toner base particles may contain an internal additive other than the magnetic powder (for example, at least one of a release agent, a colorant, and a charge control agent) as necessary. If not necessary, the external additive may be omitted. When omitting the external additive, the toner base particles correspond to the toner particles.

  The toner particles contained in the magnetic toner according to the present embodiment may be toner particles not having a shell layer (hereinafter referred to as non-capsule toner particles), or toner particles having a shell layer (hereinafter referred to as capsule toner). May be described as particles). In the capsule toner particles, the toner base particles include a core and a shell layer that covers the surface of the core. The shell layer is substantially composed of a resin. For example, by covering a core that melts at a low temperature with a shell layer having excellent heat resistance, it is possible to achieve both heat-resistant storage stability and low-temperature fixability of the toner. Additives may be dispersed in the resin constituting the shell layer. The shell layer may cover the entire surface of the core, or may partially cover the surface of the core. In order to improve the fixing property of the toner, it is preferable that the core of the capsule toner particle is substantially composed of a thermoplastic resin. In the capsule toner particles, toner base particles in non-capsule toner particles described later can be used as a core. The shell layer may be substantially composed of a thermosetting resin, may be substantially composed of a thermoplastic resin, or may contain both a thermoplastic resin and a thermosetting resin. Good.

  The magnetic toner according to this embodiment has the following basic configuration.

(Basic configuration of magnetic toner)
The magnetic toner includes a plurality of toner particles containing a crystalline polyester resin, an amorphous resin, and magnetic powder. The magnetic powder includes acicular magnetic particle powder having an aspect ratio of 2.0 or more (hereinafter referred to as acicular magnetic powder) and non-acicular magnetic particle powder having an aspect ratio of less than 2.0 (hereinafter referred to as non-magnetic powder). Described as acicular magnetic powder). The acicular magnetic particles are surface-treated with nigrosine. The residual magnetization of the magnetic toner is 7 emu / g or more and 20 emu / g or less. The aspect ratio corresponds to “maximum major axis / width perpendicular to the major axis” of the particle measured based on a microscopic image of the particle.

  In order to suppress the detachment of the magnetic powder from the toner particles while ensuring sufficient residual magnetization, fixability and chargeability of the toner, the toner may contain acicular magnetic powder and non-acicular magnetic powder. preferable. There is a tendency that the acicular magnetic powder has higher residual magnetization imparting property than the non-acicular magnetic powder. If a large amount of magnetic powder is included in the toner in order to impart sufficient residual magnetization to the toner only with the non-needle-shaped magnetic powder, it becomes difficult to ensure sufficient toner fixability. On the other hand, the dispersibility of the magnetic powder in the toner particles tends to be superior to the non-acicular magnetic powder than the acicular magnetic powder. When the toner contains only acicular magnetic powder, the acicular magnetic powder protrudes from the surface of the toner particles, and the acicular magnetic powder is easily detached from the toner particles due to friction with other objects. Also, in a high humidity environment, moisture adsorbs on the needle-shaped magnetic powder protruding from the surface of the toner particles, and the charge amount of the toner is likely to decrease. If the charge amount of the toner becomes insufficient, the image density becomes low and fog is likely to occur in image formation. In the MICR system, if the image quality of the printed identification mark is poor, there is a high possibility that the identification mark cannot be read accurately. Further, in the MICR system, in order to improve the magnetic readability of the identification mark formed of the magnetic toner, the residual magnetization of the magnetic toner is preferably 7 emu / g or more and 20 emu / g or less, and 8 emu / g or more. More preferably, it is 14 emu / g or less.

  In order to suppress the detachment of the magnetic powder from the toner particles while ensuring sufficient residual magnetization, fixability, and chargeability of the toner, the aspect ratio of the acicular magnetic particles is 3.0 to 5.0. The aspect ratio of the non-acicular magnetic particles is particularly preferably 1.0 or more and 1.5 or less. The shape of the non-acicular magnetic particles may be spherical or polyhedral.

  In order for the magnetic toner to have a remanent magnetization of 7 emu / g or more and 20 emu / g or less, the magnetic toner contains acicular magnetic powder having a saturation magnetization of 75 emu / g or more and 95 emu / g or less and a remanent magnetization of 25 emu / g or more and 50 emu / g or less. And a non-acicular magnetic powder having a saturation magnetization of 75 emu / g or more and 95 emu / g or less and a residual magnetization of 5 emu / g or more and 20 emu / g or less.

  The inventor has incorporated the crystalline polyester resin and the powder of acicular magnetic particles surface-treated with nigrosine (acicular magnetic powder) into the toner particles, whereby the acicular magnetic powder in the toner particles is contained. It has been found that dispersibility can be improved. This is probably because the crystalline polyester resin and nigrosine are appropriately compatible. Further, by incorporating nigrosine in the toner particles, the positive chargeability of the toner is improved. Hereinafter, acicular magnetic particles (untreated particles) before being surface-treated with nigrosine may be referred to as particles to be treated.

  Nigrosine is preferably present on the surface of the acicular magnetic particles in the form of particles. If the crystalline polyester resin and nigrosine are too compatible, the positive charge imparting property of nigrosine to the toner particles tends to be low. For this reason, in order to improve the positive chargeability of the toner, it is preferable that nigrosine is not excessively compatible with the crystalline polyester resin and exists on the surface of the acicular magnetic particles in the form of particles. It is preferable that an area of 10% or more and 70% or less of the entire area of the surface of the nigrosine particle is in contact with the particles to be treated (for example, ferrite particles). If the nigrosine particles are embedded too much in the particles to be treated, the positive charge imparting property of nigrosine may not be sufficiently exhibited. If the contact area between the nigrosine particles and the processing target particles is too small, the adhesive force between the nigrosine particles and the processing target particles becomes weak, and the nigrosine particles are easily detached from the processing target particles. In order to prevent the positive chargeability of the toner from becoming excessively strong, it is preferable that no nigrosine is present on the surface of the non-acicular magnetic particles.

  In order to suppress the detachment of the magnetic powder from the toner particles while ensuring sufficient residual magnetization, fixability, and chargeability of the toner, the acicular magnetic particles are ferrite particles surface-treated with nigrosine, The amount of nigrosine is preferably 2 parts by mass or more and 4 parts by mass or less with respect to 100 parts by mass of the ferrite particles.

  The saturation magnetization (unit: emu / g), remanent magnetization (unit: emu / g), and coercive force (unit: Oe (Oersted)) of the magnetic material can be measured by the following method, for example. First, the magnetic material is placed in an external magnetic field (for example, a magnetic field of 5 kOe), the magnetization of the magnetic material is saturated, and the saturation magnetization of the magnetic material is measured. Subsequently, the residual magnetic field of the magnetic material is measured by setting the external magnetic field to zero. Subsequently, the external magnetic field strength (coercive force) when the magnetic material is zeroed by applying a reverse external magnetic field to the magnetic material is measured. Note that the magnetic hysteresis curve of the magnetic material may be measured, and the saturation magnetization or the like may be read from the magnetic hysteresis curve.

In order to achieve both the heat resistant storage stability and the low-temperature fixability of the toner, it is preferable that the volume median diameter (D ₅₀ ) of the toner base particles is 4 μm or more and 9 μm or less.

  Hereinafter, a preferred example of the configuration of the non-capsule toner particles will be described. The toner base particles and the external additive will be described in order. Depending on the toner application, unnecessary components (for example, an internal additive or an external additive) may be omitted.

[Toner mother particles]
(Binder resin)
In the toner base particles, generally, the binder resin occupies most of the components (for example, 85% by mass or more). For this reason, it is considered that the properties of the binder resin greatly affect the properties of the entire toner base particles. By using a combination of a plurality of types of resins as the binder resin, the properties of the binder resin (more specifically, the hydroxyl value, acid value, Tg, Tm, etc.) can be adjusted. When the binder resin has an ester group, a hydroxyl group, an ether group, an acid group, or a methyl group, the toner base particles tend to be anionic, and when the binder resin has an amino group or an amide group. The toner base particles tend to be cationic.

  In the magnetic toner having the basic configuration described above, the toner base particles contain a crystalline polyester resin and an amorphous resin as a binder resin.

  In order to improve the low-temperature fixability of the toner, the crystallinity index of the crystalline polyester resin contained in the toner base particles is preferably 0.90 or more and 1.50 or less. A crystalline polyester resin having such a crystallinity index is excellent in sharp melt property. The crystallinity index is the ratio of the softening point (Tm) to the melting point (Mp) (= Tm / Mp). For amorphous polyester resins, it is often impossible to measure a clear Mp. The crystallinity index of the polyester resin can be adjusted by changing the type or amount of a material (for example, alcohol and / or carboxylic acid) for synthesizing the polyester resin.

  Examples of the amorphous resin include a styrene resin, an acrylic resin (more specifically, an acrylic ester polymer or a methacrylic ester polymer), an olefin resin (more specifically, a polyethylene resin). Or a thermoplastic resin such as a vinyl chloride resin, a polyvinyl alcohol, a vinyl ether resin, an N-vinyl resin, a polyester resin, a polyamide resin, or a urethane resin. Further, copolymers of these resins, that is, copolymers in which arbitrary repeating units are introduced into the resin (more specifically, styrene-acrylic acid resin or styrene-butadiene resin, etc.) are also non- It can be suitably used as a crystalline resin.

  In order to achieve both the heat resistant storage stability and the low-temperature fixability of the toner, the toner base particles preferably contain a polyester resin and / or a styrene-acrylic acid resin as an amorphous resin.

  The polyester resin is obtained by polycondensing one or more alcohols and one or more carboxylic acids. The polyester resin contains an alcohol component and an acid component. As the alcohol for synthesizing the polyester resin, for example, dihydric alcohols (more specifically, diols or bisphenols) as shown below or trihydric or higher alcohols can be suitably used. As the carboxylic acid for synthesizing the polyester resin, for example, divalent carboxylic acids or trivalent or higher carboxylic acids as shown below can be suitably used.

  Preferable examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-butene-1,4. -Diol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol.

  Preferable examples of the bisphenol include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct, or bisphenol A propylene oxide adduct.

  Preferable examples of trihydric or higher alcohols include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butane. Triol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, or 1,3,5- Trihydroxymethylbenzene is mentioned.

  As preferable examples of the divalent carboxylic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid Succinic acid, alkyl succinic acid (more specifically, n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid, etc.), or alkenyl succinic acid (more specific Specifically, n-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, or isododecenyl succinic acid, etc.) may be mentioned.

  Preferred examples of the trivalent or higher carboxylic acid include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) Examples include methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, or empole trimer acid.

  The styrene-acrylic acid resin is a copolymer of one or more styrene monomers and one or more acrylic monomers. In order to synthesize a styrene-acrylic acid resin, for example, a styrene monomer and an acrylic acid monomer as shown below can be suitably used. By using an acrylic acid monomer having a carboxyl group, a carboxyl group can be introduced into the styrene-acrylic acid resin. Further, by using a monomer having a hydroxyl group (more specifically, p-hydroxystyrene, m-hydroxystyrene, (meth) acrylic acid hydroxyalkyl ester, or the like), the hydroxyl group can be introduced into the styrene-acrylic acid resin. .

  Preferable examples of the styrene monomer include styrene, alkyl styrene (more specifically, α-methyl styrene, p-ethyl styrene, 4-tert-butyl styrene, etc.), p-hydroxy styrene, m-hydroxy styrene. , Vinyl toluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, or p-chlorostyrene.

  Preferable examples of the acrylic acid monomer include (meth) acrylic acid, (meth) acrylic acid alkyl ester, or (meth) acrylic acid hydroxyalkyl ester. Suitable examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, and (meth) acrylic. Examples include n-butyl acid, iso-butyl (meth) acrylate, or 2-ethylhexyl (meth) acrylate. Suitable examples of the (meth) acrylic acid hydroxyalkyl ester include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or (meth) acrylic. The acid 4-hydroxybutyl is mentioned.

(Coloring agent)
The toner base particles may contain a colorant (for example, a black colorant). Examples of black colorants include carbon black, oil furnace black, channel black, lamp black, acetylene black, or aniline black.

  The amount of the black colorant is preferably 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the binder resin.

(Release agent)
The toner base particles may contain a release agent. The release agent is used, for example, for the purpose of improving the fixing property or offset resistance of the toner. In order to improve the fixing property or offset resistance of the toner, the amount of the release agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

  Examples of the release agent include low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, or aliphatic hydrocarbon wax such as Fischer-Tropsch wax; oxidized polyethylene wax or a block thereof Oxides of aliphatic hydrocarbon waxes such as copolymers; plant waxes such as candelilla wax, carnauba wax, wood wax, jojoba wax, or rice wax; animal properties such as beeswax, lanolin, or whale wax Waxes; mineral waxes such as ozokerite, ceresin, or petrolatum; waxes based on fatty acid esters such as montanate ester wax or castor wax; fats such as deoxidized carnauba wax The wax portion of the ester or the whole was deoxygenated can be suitably used. One type of release agent may be used alone, or multiple types of release agents may be used in combination.

(Charge control agent)
The toner base particles may contain a charge control agent. The charge control agent is used, for example, for the purpose of improving the charge stability or charge rising property of the toner. The charge rising characteristic of the toner is an index as to whether or not the toner can be charged to a predetermined charge level in a short time.

  By adding a negatively chargeable charge control agent to the toner base particles, the anionicity of the toner base particles can be enhanced. Further, by adding a positively chargeable charge control agent to the toner base particles, the cationic property of the toner base particles can be enhanced. However, if sufficient chargeability is ensured in the toner, it is not necessary to add a charge control agent to the toner base particles.

  Examples of positively chargeable charge control agents include pyridazine, pyrimidine, pyrazine, 1,2-oxazine, 1,3-oxazine, 1,4-oxazine, 1,2-thiazine, 1,3-thiazine, 1,4- Thiazine, 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, Azine compounds such as 4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline, or quinoxaline; Azin Fast Red FC, Azin Fast Red 12BK, Azin Bai LET BO, azine brown 3G, azine light brown GR, azine dark green BH / C, azine deep black EW, azine deep black 3RL, or dyes such as nigrosine; metal salts of naphthenic acid or higher organic carboxylic acids; Quaternary ammonium salts such as alkoxylated amines; alkylamides; benzyldecylhexylmethylammonium chloride or decyltrimethylammonium chloride can be suitably used. The positively chargeable charge control agents can be used in combination of two or more. In order to improve the charge rising property of the toner, it is particularly preferable to use nigrosine and / or a quaternary ammonium salt among the positively chargeable charge control agents.

(Magnetic powder)
In the magnetic toner having the above basic configuration, the toner base particles are acicular magnetic powder (powder of acicular magnetic particles having an aspect ratio of 2.0 or more) and non-acicular magnetic powder (having an aspect ratio of less than 2.0). Non-acicular magnetic particle powder).

  Examples of the materials of the acicular magnetic powder and the non-acicular magnetic powder include, for example, ferromagnetic metals (more specifically, iron, cobalt, nickel, or alloys containing one or more of these metals), ferromagnetic materials, and the like. Metal oxides (more specifically, ferrite, magnetite, chromium dioxide, etc.) or materials subjected to ferromagnetization (more specifically, carbon materials etc. that have been rendered ferromagnetic by heat treatment) It can be used suitably.

  The acicular magnetic particles are surface-treated with nigrosine. Nigrosine comprises an aniline compound (more specifically, aniline or aniline hydrochloride) and an aromatic nitro compound (more specifically, nitrobenzene, nitrophenol, nitrocresol, etc.) and a catalyst (more specifically, Is obtained by a redox condensation reaction in the presence of iron, iron chloride, copper or the like. Nigrosine thus obtained is often a mixture containing one or more azine compounds. An azine compound is a compound containing a 6-membered ring having one or more nitrogen atoms in the ring. Preferable examples of nigrosine include azine compounds having a phenazine skeleton.

  As specific examples of nigrosine (CI Solvent Black 5, CI Solvent Black 7, and other nigrosine), commercially available products manufactured by Orient Chemical Industry Co., Ltd. are shown below. One type of commercially available product may be used alone, or two or more types of commercially available products may be mixed and used. Further, instead of or in addition to a commercially available product, nigrosine other than the commercially available product (a custom-made product or an original work) may be used.

(CI Solvent Black 5)
・ SPIRIT BLACK: “ABL”
・ NUBIAN (registered trademark) BLACK: “NH-805” / “NH-815”

(CI Solvent Black 7)
・ NIGROSINE BASE: “EX” / “EX-BP” / “SAPL”
・ SPECIAL BLACK: “EB”
・ NUBIAN BLACK: “TN-870” / “TN-877” / “TH-807”

(Other nigrosine)
BONTRON (registered trademark): “N-71” / “N-75” / “N-79”

  Nigrosine used in the surface treatment of the acicular magnetic particles may be the same as nigrosine contained in the toner base particles as an internal additive. By using these same substances, it is possible to suppress toner mother particle deterioration due to variations in charging tendency, and to improve the reliability of the toner.

  In addition to nigrosine, the acicular magnetic particles may be further surface-treated with a surface treatment agent other than nigrosine (hereinafter referred to as other surface treatment agent). Examples of other surface treatment agents include silane compounds or silicone oils.

  The surface of the acicular magnetic particles may be covered with a resin film containing nigrosine.

[External additive]
An external additive (specifically, a powder containing a plurality of external additive particles) may be adhered to the surface of the toner base particles. For example, the toner base particles (powder) and the external additive (powder) are stirred together, so that the external additive adheres (physically bonds) to the surface of the toner base particles with a physical force. The external additive is used, for example, to improve the fluidity or handleability of the toner. In order to fully perform the functions of the external additive while suppressing the detachment of the external additive particles from the toner particles, the amount of the external additive (if multiple types of external additive particles are used, The total amount of external additive particles) is preferably 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the toner base particles. In order to improve the fluidity or handleability of the toner, the particle diameter of the external additive is preferably 0.01 μm or more and 1.0 μm or less.

  The external additive particles are preferably inorganic particles such as silica particles or metal oxides (more specifically, alumina, zirconia, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, barium titanate, etc.). Particles are particularly preferred. However, resin particles may be used as the external additive particles. One type of external additive particles may be used alone, or a plurality of types of external additive particles may be used in combination.

[Toner Production Method]
In order to easily and suitably manufacture the magnetic toner having the above-described basic configuration, for example, a toner manufacturing method including the following melt-kneading step, pulverizing step, washing step, drying step, and external addition step is preferable.

(Melting and kneading process)
Hereinafter, an example of the melt-kneading process will be described. In the melt-kneading step, a toner material containing a crystalline polyester resin, an amorphous resin, and magnetic powder (for example, a crystalline polyester resin, an amorphous polyester resin, a colorant, a release agent, a charge control agent, and a magnetic powder ) To obtain a mixture. The magnetic powder used has a configuration defined by the basic configuration described above. Specifically, the magnetic powder includes acicular magnetic powder and non-acicular magnetic powder. The acicular magnetic particles are surface-treated with nigrosine. For example, a mixture of acicular magnetic powder and nigrosine is mixed at a suitable rotation speed (eg, 800 rpm to 2800 rpm) using a mixing device (eg, FM mixer) for a suitable time (eg, 30 seconds to 10 minutes). By stirring, the needle-like magnetic particles can be easily surface treated with nigrosine. Also, by mixing nigrosine and other surface treatment agent in the liquid, adding acicular magnetic particles to the liquid and stirring the liquid, the acicular magnetic particles are mixed with nigrosine and the other surface treatment agent. You may surface-treat with. For mixing the toner material, a mixing device (for example, FM mixer) can be suitably used. As the toner material, a master batch containing a binder resin and a colorant may be used.

  Subsequently, the obtained mixture is melt-kneaded to obtain a melt-kneaded product. For melt kneading of the mixture, a twin-screw extruder, a three-roll kneader, or a two-roll kneader can be suitably used.

(Crushing process)
Hereinafter, an example of the grinding step will be described. First, the melt-kneaded product is solidified by cooling using a cooling and solidifying device such as a drum flaker. Subsequently, the obtained solidified product is roughly pulverized using the first pulverizer. Thereafter, the obtained coarsely pulverized product is further pulverized using a second pulverizer to obtain a powder. The obtained powder (pulverized product) may be classified using a classifier (for example, an air classifier).

(Washing process)
After the pulverization step, the toner base particles may be washed using, for example, water. As a method for cleaning the toner base particles, for example, the dispersion containing the toner base particles is solid-liquid separated to collect the wet cake-like toner base particles, and the collected wet cake-like toner base particles are washed with water. Is preferred. As a method for cleaning the toner base particles, a method is preferred in which the toner base particles in the dispersion containing the toner base particles are settled, the supernatant liquid is replaced with water, and the toner base particles are redispersed in water after the replacement.

(Drying process)
After the cleaning step, the toner base particles may be dried. For example, the toner base particles can be dried using a dryer (more specifically, a spray dryer, a fluidized bed dryer, a vacuum freeze dryer, a vacuum dryer, or the like). In order to suppress aggregation of the toner base particles during drying, it is preferable to dry the toner base particles using a spray dryer. In the case of using a spray dryer, for example, by spraying a dispersion liquid in which an external additive (more specifically, silica particles or the like) is dispersed onto the toner base particles, the drying step and the external addition step described later are performed simultaneously. It becomes possible to do.

(External addition process)
An external additive may be attached to the surface of the toner base particles. By using a mixer, the toner base particles and the external additive are mixed under conditions that prevent the external additive from being embedded in the toner base particles, thereby allowing the external additive to adhere to the surface of the toner base particles. .

  Through the above process, a toner containing a large number of toner particles can be produced. Note that unnecessary steps may be omitted. For example, when a commercially available product can be used as a material as it is, the step of preparing the material can be omitted by using a commercially available product. In the case where the external additive is not attached to the surface of the toner base particles (the external addition step is omitted), the toner base particles correspond to the toner particles. In order to obtain a predetermined compound, a salt, ester, hydrate, or anhydride of the compound may be used as a raw material. In order to produce the toner efficiently, it is preferable to form a large number of toner particles simultaneously. The toner particles produced at the same time are considered to have substantially the same configuration.

  Examples of the present invention will be described. Table 1 shows toners TA-1 to TA-6 and TB-1 to TB-3 (each magnetic toner for MICR) according to Examples or Comparative Examples. Table 2 shows ferrite particles used in the production of the toners shown in Table 1. Table 3 shows the surface treatment conditions of the ferrite particles in the acicular magnetic powder.

  Hereinafter, the production methods, evaluation methods, and evaluation results of the toners TA-1 to TA-6 and TB-1 to TB-3 will be described in order. In the evaluation in which an error occurs, a considerable number of measurement values with sufficiently small errors are obtained, and the arithmetic average of the obtained measurement values is used as the evaluation value.

[Toner Production Method]
(Preparation of crystalline polyester resin)
As a crystalline polyester resin, “HDK-C14” manufactured by Kao Corporation was prepared.

(Preparation of non-crystalline polyester resin)
By reacting a bisphenol A ethylene oxide adduct (specifically, an alcohol obtained by adding ethylene oxide with bisphenol A as a skeleton) with an acid having a polyfunctional group (specifically, terephthalic acid), an amorphous polyester resin is obtained. Synthesized.

(Preparation of non-acicular magnetic powder)
As the non-acicular magnetic powder, ferrite powder powder having physical properties shown in Table 2 was prepared. The aspect ratio of the non-acicular magnetic particles contained in the non-acicular magnetic powder was 1.3 (see Table 2). The shape of the non-acicular magnetic particles was polyhedral.

(Preparation of acicular magnetic powder)
The surface treatment shown in Table 3 was performed on the powder of ferrite particles (treatment target particles) having the physical properties shown in Table 2 to obtain acicular magnetic powders MA to MD. Specifically, using an FM mixer (“FM-20B” manufactured by Nippon Coke Kogyo Co., Ltd.), 1000 g of ferrite particles (powder), 10 g of a trimethoxysilane compound (γ-glycidoxypropylene trimethoxysilane), The amount of nigrosine shown in 3 ("BONTRON N-71" manufactured by Orient Chemical Co., Ltd.) was mixed for 5 minutes at a rotation speed of 500 rpm. For example, in the preparation of the acicular magnetic powder MA, 30 g of nigrosine was added to 1000 g of ferrite particles (powder) (see Table 3). In addition, nigrosine was not added in the preparation of the acicular magnetic powder MD. The aspect ratio of the acicular magnetic particles contained in each of the acicular magnetic powders MA to MD was 3.6 as it was before the surface treatment (see Table 2).

(Preparation of toner base particles)
Using an FM mixer ("FM-20B" manufactured by Nippon Coke Kogyo Co., Ltd.), 2 parts by mass of a crystalline resin (crystalline polyester resin prepared as described above) and an amorphous resin (prepared as described above) Amorphous polyester resin), 5 parts by mass of a colorant (carbon black: “MA-100” manufactured by Mitsubishi Chemical Corporation), and a release agent (ester wax: “Nissan Electol (registered trademark)” manufactured by NOF Corporation. WEP-3 ") 4 parts by mass, 1 part by mass of a charge control agent (Nigrosine:" BONTRON N-71 "manufactured by Orient Chemical Industry Co., Ltd.), and acicular magnetic powder (determined for each toner, as shown in Table 1 Any of the acicular magnetic powders MA to MD) and non-acicular magnetic powder (non-acicular magnetic powder prepared as described above) were mixed at a temperature of 40 ° C. and a rotation speed of 1500 rpm for 5 minutes. The amount of each of the non-crystalline resin (non-crystalline polyester resin), acicular magnetic powder and non-acicular magnetic powder was as shown in Table 1. For example, in the production of the toner TA-1, 38 parts by mass of an amorphous polyester resin, 40 parts by mass of acicular magnetic powder MA, and 10 parts by mass of non-acicular magnetic powder (ferrite particles) were added. Further, in the production of the toner TB-1, 38 parts by mass of the amorphous polyester resin and 50 parts by mass of the acicular magnetic powder MA were added, and the non-acicular magnetic powder was not added.

Subsequently, the obtained mixture was melt-kneaded using a twin-screw extruder (“PCM-30” manufactured by Ikegai Co., Ltd.). Thereafter, the obtained kneaded material was cooled. As a result, a plate-like kneaded product was obtained. Subsequently, the obtained plate-shaped kneaded product was coarsely pulverized using a pulverizer (“Rohtoplex (registered trademark)” manufactured by Hosokawa Micron Corporation). Subsequently, the obtained coarsely pulverized product was finely pulverized using a pulverizer (“Turbo Mill RS type” manufactured by Freund Turbo Co., Ltd.). Subsequently, the obtained finely pulverized product was classified using a classifier (“Elbow Jet EJ-LABO type” manufactured by Nippon Steel Mining Co., Ltd.). As a result, toner mother particles having a volume median diameter (D ₅₀ ) of 6 μm were obtained.

(External addition process)
Using an FM mixer (“FM-20B” manufactured by Nippon Coke Industries Co., Ltd.) under the condition of a rotational speed of 1500 rpm, 100 parts by mass of toner base particles and first silica particles (“CAB-O-SIL (registered by Cabot Corporation)”) (Trademark) TG-7120 ") 1.0 part by mass, second silica particles (" MS-220NF "manufactured by Teika Co., Ltd.) 0.5 parts by mass, and first titanium oxide particles (" EC- "manufactured by Titanium Industry Co., Ltd.). 100 ") 1.2 parts by mass and 0.4 parts by mass of second titanium oxide particles (" ET-808 "manufactured by Ishihara Sangyo Co., Ltd.) were mixed for 5 minutes. As a result, external additives (silica particles and titanium oxide particles) adhered to the surface of the toner base particles. Then, sieving was performed using a 300 mesh sieve (aperture 48 μm). As a result, magnetic toners (toners TA-1 to TA-6 and TB-1 to TB-3 shown in Table 1) containing a large number of toner particles (magnetic particles) were obtained.

  Regarding the toners TA-1 to TA-6 and TB-1 to TB-3 obtained as described above, the measurement results of the residual magnetization are as shown in Table 1. For example, regarding the toner TA-1, the residual magnetization was 12.9 emu / g. The measurement conditions of the remanent magnetization were as follows.

<Measurement conditions of remanent magnetization>
・ Measuring device: High-sensitivity vibration sample type magnetometer (“VSM-P7” manufactured by Toei Kogyo Co., Ltd.)
Measurement mode: 3/4 loop Measurement magnetic field range: -5 kOe to +5 kOe
・ Sample amount: Approximately 55mg

[Evaluation method]
The evaluation method of each sample (toners TA-1 to TA-6 and TB-1 to TB-3) is as follows.

(Dispersibility of magnetic powder)
The toner particles contained in the sample (toner) were cut using an ultramicrotome (“MT-6000XL” manufactured by RMC), and the cross section of the toner particles was observed using an electron microscope. The dispersibility of the magnetic powder was evaluated according to the following criteria.
○ (Good): No lump of magnetic powder was observed.
Δ (Normal): A small lump of magnetic powder was observed.
X (bad): A large lump of magnetic powder was observed.

(Fixability)
As an evaluation machine, a monochrome printer (“FS-4020DN” manufactured by Kyocera Document Solutions Inc.) was used. About 200 g of sample (toner) was set in the developing device of the evaluation machine in the installation mode. The fixing temperature of the evaluation machine was set to 180 ° C.

An image having a printing rate of 90% was formed on an evaluation paper (“Classic Crest (registered trademark)” manufactured by Nina Co., Ltd.) under the environment of a temperature of 23 ° C. and a humidity of 55% RH. Thereafter, the paper on which the image was formed was passed through a fixing device of an evaluation machine. Subsequently, using a reflection densitometer (“SpectroEye (registered trademark)” manufactured by X-Rite), the image density (hereinafter referred to as pre-rubbing ID) of the image on the paper passed through the fixing device was measured. Subsequently, using a 1 kg weight coated with a fabric, the image on the evaluation paper was rubbed 10 times. Subsequently, using a reflection densitometer (SpectroEye), the image density of the image on the evaluation paper (hereinafter referred to as post-rubbing ID) was measured. Subsequently, the fixing rate (unit:%) was determined according to the formula “fixing rate = 100 × ID after rubbing / ID before rubbing”. The fixing rate indicates how much the image density (ID) decreases after rubbing, based on the image density (ID) before rubbing. That is, the fixing rate is an index indicating the ratio of the toner that is sufficiently fixed in the toner constituting the image.
A (very good): The fixing rate was 95% or more.
○ (Good): Fixing rate was 90% or more and less than 95%.
X (Poor): Fixing rate was less than 90%.

(Image density and fog density)
Each of the image density and the fog density was evaluated in an N / N environment (temperature 23 ° C. and humidity 55% RH) and in an H / H environment (temperature 28 ° C. and humidity 80% RH). Using a monochrome printer (“FS-2020DN” manufactured by Kyocera Document Solutions Co., Ltd.) with a sample (toner) set under a predetermined environment (N / N environment or H / H environment), including a solid part and a blank part Sample images were printed on evaluation paper. Then, using a reflection densitometer (“RD914” manufactured by X-Rite), the reflection density (ID: image density) of the solid portion of the sample image on the printed paper was measured. Further, the reflection density was measured for each of the blank portion of the sample image on the printed paper and the unprinted base paper (unprinted paper) using the reflection densitometer (RD914). Then, the fog density (FD) was calculated based on the following equation.
FD = (reflection density of blank area) − (reflection density of unprinted paper)

The image density (ID) was evaluated according to the following criteria.
A (very good): The image density (ID) was 1.30 or more.
○ (good): The image density (ID) was 1.20 or more and less than 1.30.
Δ (Normal): The image density (ID) was 1.10 or more and less than 1.20.
X (Poor): Image density (ID) was less than 1.10.

The fog density (FD) was evaluated according to the following criteria.
A (very good): The fog density (FD) was less than 0.010.
○ (Good): The fog density (FD) was 0.010 or more and less than 0.020.
Δ (Normal): The fog density (FD) was 0.020 or more and less than 0.100.
X (Poor): The fog density (FD) was 0.100 or more.

(Magnetic readability)
An E13B font was printed on the evaluation paper using a monochrome printer (“FS-2020DN” manufactured by Kyocera Document Solutions Co., Ltd.) in which a sample (toner) was set in an environment of a temperature of 23 ° C. and a humidity of 55% RH. Using a MICR reader ("MICR Qualifier" manufactured by RDM), the reading rate of the printed font was measured. When the reading rate was 90% or more and less than 200%, it was evaluated as ◯ (good), and when the reading rate was less than 90% or 200% or more, it was evaluated as x (not good). The reading rate of 100% corresponds to the reading rate of the standard test pattern.

[Evaluation results]
Table 4 shows the evaluation results of toners TA-1 to TA-6 and TB-1 to TB-3. Table 4 shows dispersibility of magnetic powder (evaluation result by microscopic observation), fixability (fixing rate), image evaluation under N / N environment (image density and fog density), and image evaluation under H / H environment. The measured values of (image density and fog density) and magnetic readability (reading rate) are shown.

  The toners TA-1 to TA-6 (magnetic toners according to Examples 1 to 6) each had the above-described basic configuration. Specifically, in toners TA-1 to TA-6, each toner particle contained a crystalline polyester resin, an amorphous resin, and magnetic powder. As shown in Table 2, the magnetic powder includes acicular magnetic powder (powder of acicular magnetic particles having an aspect ratio of 2.0 or more) and non-acicular magnetic powder (non-acicular shapes having an aspect ratio of less than 2.0). Magnetic particle powder). The acicular magnetic particles were surface-treated with nigrosine. Nigrosine was present on the surface of acicular magnetic particles in the form of particles. In addition, nigrosine was not present on the surface of the non-acicular magnetic particles. As shown in Table 1, the residual magnetizations of the toners TA-1 to TA-6 were 7 emu / g or more and 20 emu / g or less.

  As shown in Table 4, each of the toners TA-1 to TA-6 has magnetic powder dispersibility, fixability, image evaluation under an N / N environment, image evaluation under an H / H environment, and magnetism. Excellent readability.

  Toner TB-2 (magnetic toner according to Comparative Example 2) was inferior to toners TA-1 to TA-6 in terms of dispersibility of the magnetic powder and image evaluation. In toner TB-2, it is considered that leakage occurred due to poor dispersion of the magnetic powder, and the charge amount of the toner became insufficient.

  In the production method of the toner TA-1, an amorphous styrene-acrylic acid resin (specifically, a copolymer of styrene and n-butyl acrylate is used instead of an amorphous polyester resin as an amorphous resin. Even when the polymer was used, good results (◯ or ◎) were obtained in all evaluations. However, regarding the evaluation of fixability, it was better to use an amorphous polyester resin.

  The magnetic toner according to the present invention can be used for forming an image in, for example, a copying machine, a printer, or a multifunction machine.

Claims (9)

A magnetic toner comprising a plurality of toner particles containing a crystalline polyester resin, an amorphous resin, and magnetic powder,
The magnetic powder includes acicular magnetic powder that is a powder of acicular magnetic particles having an aspect ratio of 2.0 or more, and non-acicular magnetic powder that is a powder of non-acicular magnetic particles having an aspect ratio of less than 2.0. Including
The acicular magnetic particles are surface-treated with nigrosine,
The residual magnetization of the magnetic toner Ri der following 7emu / g or more 20 emu / g,
A magnetic toner in which nigrosine is not present on the surface of the non-acicular magnetic particles .   The magnetic toner according to claim 1, wherein the non-crystalline resin is a non-crystalline polyester resin. The toner particles are
Toner base particles containing the crystalline polyester resin, the amorphous resin, and the magnetic powder;
An external additive attached to the surface of the toner base particles;
The magnetic toner according to claim 1, comprising:   The magnetic toner according to claim 1, wherein the nigrosine is present on the surface of the acicular magnetic particles in a particle state.   The magnetic toner according to claim 1, wherein the residual magnetization of the magnetic toner is 8 emu / g or more and 14 emu / g or less.   Acicular magnetic powder having a saturation magnetization of 75 emu / g to 95 emu / g and a residual magnetization of 25 emu / g to 50 emu / g, a saturation magnetization of 75 emu / g to 95 emu / g and a residual magnetization of 5 emu / g to 20 emu / g. The magnetic toner according to claim 1, which is a mixture with non-acicular magnetic powder. The acicular magnetic particles are ferrite particles surface-treated with nigrosine,
7. The magnetic toner according to claim 1, wherein an amount of the nigrosine is 2 parts by mass or more and 4 parts by mass or less with respect to 100 parts by mass of the ferrite particles. The aspect ratio of the acicular magnetic particles is 3.0 or more and 5.0 or less,
The magnetic toner according to claim 1, wherein an aspect ratio of the non-acicular magnetic particles is 1.0 or more and 1.5 or less. The magnetic toner is MICR toner, magnetic toner according to any one of claims 1-8.