JP7427986B2 - Toner for developing electrostatic latent images - Google Patents

Description

The present invention relates to a toner for developing electrostatic latent images. More specifically, the present invention relates to an electrostatic latent image developing toner containing fine metal particles that can suppress the occurrence of toner scattering even during continuous printing.

In recent years, even in image formation using electrophotographic processes, high value-added images such as those seen in the commercial printing field have been output in response to various customer needs. For example, one aspect of this is to output an image with a metallic luster using a glitter toner as a toner for developing an electrostatic latent image (hereinafter also simply referred to as "toner") (for example, as described in Patent Document 1). reference).

As the glitter toner, for example, a toner containing a binder resin and a metal pigment, which is fine metal particles such as aluminum, brass, bronze, nickel, stainless steel, zinc, etc., is used. Since the electrical properties of the metal pigment are significantly different from those of the binder resin, in a glitter toner containing the metal pigment, there will be parts where the metal pigment is present near the toner surface and parts where it is not present. As a result, there is a problem in that the charging characteristics of the toner surface tend to become non-uniform.

When such a glitter toner is used in an electrophotographic process, the charge amount distribution of the toner tends to spread during continuous printing, resulting in problems such as toner scattering. Toner scattering causes problems of image forming defects such as contamination of the image forming apparatus and fogging of printed matter.

Japanese Patent Application Publication No. 2017-62315

The present invention has been made in view of the above-mentioned problems and circumstances, and an object to be solved is to provide an electrostatic latent image developing toner containing fine metal particles that can suppress the occurrence of toner scattering even during continuous printing. The objective is to provide toner for use in

In order to solve the above problems, the present inventors, in the process of studying the causes of the above problems, discovered that toner base particles containing a binder resin and metal fine particles and a number average primary It has been discovered that it is possible to provide a toner for developing electrostatic latent images that can suppress the occurrence of toner scattering even during continuous printing by containing an external additive containing fine alumina particles having a particle size within a predetermined range, and has thus arrived at the present invention. Ta. That is, the problems related to the present invention are solved by the following means.

1. A toner for developing an electrostatic latent image, comprising toner base particles containing a binder resin and fine metal particles, and an external additive attached to the surface of the toner base particles,
The metal fine particles contained within the toner base particles include aluminum fine particles having a volume-based median diameter within a range of 150 to 500 nm;
A toner for developing electrostatic latent images, characterized in that the external additive contains alumina fine particles having a number average primary particle size within a range of 8 to 30 nm.

2. 2. The toner for developing electrostatic latent images according to item 1, wherein the amount of the alumina fine particles attached is within the range of 0.05 to 2.0 parts by mass based on 100 parts by mass of the toner base particles. .

3. 2. The toner for developing electrostatic latent images according to item 1 or 2, wherein the alumina fine particles are surface-modified with a silane compound having a structure represented by the following general formula (1).
General formula (1): X-Si(OR) ₃
[In formula (1), X represents an alkyl group having 2 to 8 carbon atoms. Each R independently represents a methyl group or an ethyl group. ]

4. 4. The toner for developing electrostatic latent images according to item 3, wherein the surface-modified alumina fine particles have a carbon content in a range of 1.0 to 8.0% by mass.

5. Any one of items 1 to 4, wherein the average adhesion strength of the alumina fine particles on the particle surface of the toner represented by the following formula (A) is within the range of 45 to 85%. The toner for developing an electrostatic latent image as described in .
Adhesion strength of alumina fine particles=(Al atom abundance ratio in toner after ultrasonic treatment/Al atom abundance ratio in toner before ultrasonic treatment)×100...Formula (A)
However, the toner after ultrasonic treatment in formula (A) is obtained by moistening 3 g of the toner before ultrasonic treatment as a specimen with 40 g of a 0.2% by mass aqueous solution of polyoxyethylphenyl ether in a 100 mL plastic cup. After applying ultrasonic energy at a current value of 60 μA (50 W) for 3 minutes using an ultrasonic homogenizer, filtration was performed using a filter with an opening of 1 μm, washed with 60 mL of pure water, and dried. This is the later toner.
The Al atom abundance ratio in formula (A) is a value calculated by the following formula (B) based on the peak area of each atom obtained by measuring the surface of the toner particle as a specimen by X-ray electron spectroscopy. be.
(Al/(C+O+Si+Ti+Al))×100 atom%...Formula (B)

By means of the above means of the present invention, it is possible to provide an electrostatic latent image developing toner containing fine metal particles that can suppress the occurrence of toner scattering even during continuous printing. Although the mechanism of expression or action of the effects of the present invention is not clear, it is speculated as follows.

The toner for developing electrostatic latent images of the present invention comprises toner base particles containing a binder resin and fine metal particles, and a number-average primary particle diameter within the range of 8 to 30 nm, which is attached to the surface of the toner base particles. Contains an external additive containing certain alumina particles. In toner base particles containing a binder resin and metal fine particles, the metal fine particles tend to be unevenly distributed because their electrical properties are significantly different from those of the binder resin. Specifically, in the toner base particles, the particle surface tends to be convex in areas where metal fine particles are present, and the particle surface tends to be concave in areas where metal fine particles are not present.

The alumina fine particles used as an external additive have electrical properties similar to those of the metal fine particles contained in the toner base particles, and are likely to selectively adhere to the recesses of the toner base particles when attached to the surface of the toner base particles. It is presumed that by configuring the toner so that metal fine particles are present in the convex portions of the toner base particle surface and alumina fine particles having electrical characteristics similar to the metal fine particles are present in the concave portions, the charging characteristics of the toner surface become uniform. In addition, because the alumina fine particles used as an external additive have the above-mentioned specific particle size, they are fixed in the recesses on the surface of the toner base particles and are difficult to move on the toner surface. can be expected to stably exhibit the above effects.

The toner for developing electrostatic latent images of the present invention includes toner base particles containing a binder resin and fine metal particles, and an external additive attached to the surface of the toner base particles. The external additive is characterized in that it contains fine alumina particles having a number average primary particle size within the range of 8 to 30 nm. This feature is a technical feature common to each of the embodiments described below.

In an embodiment of the present invention, from the viewpoint of achieving higher effects of the present invention, the amount of the alumina fine particles attached is within a range of 0.05 to 2.0 parts by mass based on 100 parts by mass of the toner base particles. It is preferable that

In an embodiment of the present invention, from the viewpoint of further enhancing the effect of the present invention by optimizing the adhesion of the alumina fine particles to the toner base particles and the cohesiveness of the alumina fine particles with each other, the alumina fine particles are Preferably, the surface is modified with a silane compound having a structure represented by formula (1). Furthermore, the carbon content in the surface-modified alumina fine particles is preferably within the range of 1.0 to 8.0% by mass.

In an embodiment of the present invention, from the viewpoint of further enhancing the effect of the present invention by optimizing the adhesion of the alumina fine particles to the toner base particles, the toner particle surface represented by the above formula (A) is provided. It is preferable that the average adhesion strength of the alumina fine particles is within the range of 45 to 85%.

Hereinafter, the present invention, its constituent elements, and forms and aspects for carrying out the present invention will be described in detail. In this application, "~" is used to include the numerical values described before and after it as a lower limit value and an upper limit value.

[Overview of toner for developing electrostatic latent images]
The toner for developing electrostatic latent images according to the present invention includes toner base particles containing a binder resin and fine metal particles, and an external additive attached to the surface of the toner base particles. The method is characterized in that the external additive contains alumina fine particles having a number average primary particle size within a range of 8 to 30 nm.

<Toner base particles>
The toner base particles of the toner of the present invention are particles containing a binder resin and fine metal particles, and may also contain internal additives such as a colorant, a release agent, and a charge control agent.

(Binder resin)
The binder resin used in the present invention is not particularly limited, but it is preferable that the binder resin contains styrene-acrylic resin because charging can be easily controlled.

The styrene-acrylic resin mentioned here is formed by addition polymerization of a styrene monomer and a (meth)acrylic acid ester monomer. In addition to styrene represented by the structural formula of CH ₂ ═CH—C ₆ H ₅ , the styrene monomers include those having a structure having a known side chain or functional group in the styrene structure. In addition, the (meth)acrylic acid ester monomer mentioned here is an acrylic acid ester compound represented by CH ₂ = CHCOOR (R is an alkyl group), or an acrylic acid ester compound represented by CH ₂ = CCH ₃ COOR (R is an alkyl group). In addition to the expressed methacrylic ester compounds, the compounds include ester compounds having known side chains or functional groups in their structures, such as acrylic ester derivatives and methacrylic ester derivatives.

In addition, in this specification, "(meth)acrylic acid" means at least one of acrylic acid and methacrylic acid. "(Meth)acrylate" means at least one of acrylate and methacrylate. Specific examples of styrene monomers and (meth)acrylic acid ester monomers that can form styrene-acrylic resin are shown below, and they are used to form the styrene-acrylic resin unit used in the present invention. Possibilities are not limited to those shown below.

Specific examples of styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethyl Examples include styrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, and derivatives thereof. It will be done. These styrene monomers can be used alone or in combination of two or more.

Specific examples of (meth)acrylic acid ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl ( meth)acrylate, isobutyl(meth)acrylate, n-octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, stearyl(meth)acrylate, lauryl(meth)acrylate, phenyl(meth)acrylate, diethylaminoethyl methacrylate, dimethylamino Examples include ethyl methacrylate.

In addition, as the polymerizable monomer, a third polymerizable monomer can also be used in addition to the above. Examples of the third polymerizable monomer include acid monomers such as acrylic acid, methacrylic acid, maleic anhydride, and vinyl acetic acid, as well as acrylamide, methacrylamide, acrylonitrile, ethylene, propylene, butylene vinyl chloride, N-vinylpyrrolidone, and Examples include butadiene.

As the polymerizable monomer, a polyfunctional vinyl monomer may also be used. Examples of polyfunctional vinyl monomers include di(meth)acrylates of diols such as ethylene glycol, propylene glycol, butylene glycol, and hexylene glycol, and di(meth)acrylates of tertiary or higher alcohols such as pentaerythritol and trimethylolpropane. (meth)acrylate, divinylbenzene, etc.

The weight average molecular weight (Mw) of the styrene-acrylic resin is preferably within the range of 10,000 to 100,000 as Mw based on polystyrene measured by gel permeation chromatography (GPC).

The method for producing styrene-acrylic resin is not particularly limited, and any polymerization initiator such as peroxide, persulfide, persulfate, or azo compound commonly used for polymerization of the above monomers is used, and bulk polymerization is performed. , solution polymerization, emulsion polymerization method, miniemulsion method, dispersion polymerization method, and other known polymerization methods. Furthermore, a commonly used chain transfer agent can be used for the purpose of adjusting the molecular weight. The chain transfer agent is not particularly limited, and examples include alkyl mercaptans such as n-octyl mercaptan, mercapto fatty acid esters such as n-octyl-3-mercaptopropionate, and the like.

The content of the styrene-acrylic resin is preferably 70% by mass or more based on the total amount of the binder resin. Styrene-acrylic resin is an amorphous resin. The binder resin may contain an amorphous resin other than styrene-acrylic resin, if necessary. Furthermore, in the present invention, the binder resin may contain a crystalline resin in addition to the amorphous resin. When the binder resin contains a crystalline resin, it can contribute to improving the low-temperature fixability of the toner.

The crystalline resin in the present invention refers to a resin that does not show a step-like endothermic change but has a clear endothermic peak in differential scanning calorimetry (DSC). A clear endothermic peak specifically refers to a peak in which the half-width of the endothermic peak is within 15°C when measured at a heating rate of 10°C/min in differential scanning calorimetry (DSC). do. Furthermore, the amorphous resin according to the present invention is a resin that does not have a melting point and has a relatively high glass transition temperature (Tg) when differential scanning calorimetry (DSC) is performed on the resin.

Differential scanning calorimetry (DSC) can be performed using, for example, DSC-7 differential scanning calorimeter (manufactured by PerkinElmer) and TAC7/DX thermal analyzer controller (manufactured by PerkinElmer). Specifically, 4.50 mg of the sample was sealed in an aluminum pan (KIT No. 0219-0041), and this was set in the sample holder of "DSC-7", and the empty aluminum pan was used for reference measurements. Then, Heat-Cool-Heat temperature control was performed under the measurement conditions of a measurement temperature of 0 to 200°C, a heating rate of 10°C/min, and a cooling rate of 10°C/min. Obtain data in Heat. The melting point is the temperature at the top of the endothermic peak.

Examples of crystalline resins include crystalline polyester resins and crystalline vinyl resins. Although not particularly limited, crystalline polyester resin is preferable in order to improve low-temperature fixing properties, and is produced by a polycondensation reaction between a divalent or higher carboxylic acid (polyvalent carboxylic acid) and a divalent or higher alcohol (polyhydric alcohol). Any known polyester resin that can be obtained can be used.

Polyvalent carboxylic acid is a compound having two or more carboxy groups in one molecule, and alkyl esters, acid anhydrides, and acid chlorides of polyvalent carboxylic acid can be used.

Examples of polyhydric carboxylic acids include oxalic acid, succinic acid, maleic acid, adipic acid, β-methyladipic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, and fumaric acid. Acid, citraconic acid, diglycolic acid, cyclohexane-3,5-diene-1,2-dicarboxylic acid, malic acid, citric acid, hexahydroterephthalic acid, malonic acid, pimelic acid, tartaric acid, mucinic acid, phthalic acid, isophthalic acid. Acid, terephthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-carboxyphenylacetic acid, p-phenylenediacetic acid, m-phenylene diglycolic acid, p-phenylene diglycolic acid, o-phenylene diglycolic acid, diphenyl Divalent compounds such as acetic acid, diphenyl-p,p'-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, anthracene dicarboxylic acid, dodecenyl succinic acid, etc. Carboxylic acid: May be combined with trivalent or higher carboxylic acids such as trimellitic acid, pyromellitic acid, naphthalenetricarboxylic acid, naphthalenetetracarboxylic acid, pyrenetricarboxylic acid, and pyrenetetracarboxylic acid.

Polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, butanediol, diethylene glycol, hexanediol, cyclohexanediol, octanediol, and nonanediol. , decanediol, dodecanediol, dihydric alcohols such as ethylene oxide adduct of bisphenol A, propylene oxide adduct of bisphenol A; glycerin, pentaerythritol, hexamethylolmelamine, hexaethylolmelamine, tetramethylolbenzoguanamine, tetraethylolbenzoguanamine Examples include polyols having a valence of 3 or more.

As the catalyst for synthesizing the crystalline polyester resin, various conventionally known catalysts can be used, such as esterification catalysts.

Examples of the esterification catalyst include tin compounds such as dibutyltin oxide and tin(II) 2-ethylhexanoate, and titanium compounds such as titanium diisopropylate bistriethanolaminate and titanium tetraisopropoxide. Examples include gallic acid. The amount of the esterification catalyst used is preferably 0.01 to 1.5 parts by mass, and preferably 0.1 to 1. .0 part by mass is more preferred. The amount of the esterification promoter used is preferably 0.001 to 0.5 parts by mass, and 0.01 to 0.5 parts by mass, based on 100 parts by mass of the total amount of polyhydric alcohol, polycarboxylic acid, and bireactive monomer components. 0.1 part by mass is more preferable.

Examples of the combination of polycarboxylic acid and polyhydric alcohol for forming the crystalline polyester resin that can be used in the present invention include 1,12-dodecanediol (12 carbon atoms) and sebacic acid (10 carbon atoms); Ethylene glycol (2 carbon atoms) and sebacic acid (10 carbon atoms), 1,6-hexanediol (6 carbon atoms) and 1,10-decanedicarboxylic acid (12 carbon atoms), 1,9-nonanediol (carbon atoms 9) and 1,10-decanedicarboxylic acid (12 carbon atoms), 1,6-hexanediol (6 carbon atoms), sebacic acid (10 carbon atoms), 1,6-hexanediol (6 carbon atoms), and 1, Examples include 12-dodecanedicarboxylic acid (14 carbon atoms).

The weight average molecular weight (Mw) of the crystalline polyester resin is preferably 2,000 to 20,000. When the Mw of the crystalline polyester resin is within the above range, the resulting toner does not have a low melting point as a whole particle and has excellent blocking resistance and low-temperature fixability. Note that the Mw is a polystyrene-based Mw measured by GPC.

Further, the melting point Tm of the crystalline polyester resin is preferably within the range of 50 to 120°C, more preferably within the range of 60 to 90°C. It is preferable that the melting point Tm of the crystalline polyester resin is within the range of 50 to 120° C. because appropriate low-temperature fixing properties and fixing separation properties can be obtained.

The melting point Tm of the crystalline polyester resin can be measured using a differential calorimeter (DSC). For example, DSC measurement is performed under Heat-Cool-Heat temperature control at a measurement temperature of 0 to 200°C, a heating rate of 10°C/min, and a cooling rate of 10°C/min. The melting point Tm is the temperature at the top of the endothermic peak in the second heat.

In addition, it is more preferable that the crystalline polyester resin is a hybrid crystalline polyester resin containing an amorphous resin other than the crystalline polyester resin as a unit. The amorphous resin unit is preferably composed of the same type of resin as the amorphous resin contained in the binder resin, that is, a resin other than the hybrid resin. By hybridizing in such a form, the affinity between the crystalline polyester resin and the binder resin increases, and the hybrid resin becomes more easily incorporated into the amorphous resin. As a result, since a crystalline polyester unit that easily absorbs moisture is present inside the toner matrix, the adhesion between toner particles is prevented from increasing due to moisture absorption, and cleaning performance is further improved.

Here, "the same kind of resin" means that a characteristic chemical bond is commonly contained in the repeating unit. Here, "characteristic chemical bonds" are described in the National Institute for Materials Science (NIMS) Substances and Materials Database (http://polymer.nims.go.jp/PoLyInfo/guide/jp/term_polymer.html) According to the "Polymer Classification" of Namely, polyacrylic, polyamide, polyanhydride, polycarbonate, polydiene, polyester, polyhaloolefin, polyimide, polyimine, polyketone, polyolefin, polyether, polyphenylene, polyphosphazene, polysiloxane, polystyrene, polysulfide, polysulfone, polyurethane, polyurea. The chemical bonds that make up the polymers classified by a total of 22 types, including polyvinyl, polyvinyl, and other polymers, are referred to as "characteristic chemical bonds."

The content of the crystalline resin contained in the toner base particles of the present invention is preferably 1% by mass or more and 30% by mass or less based on the total amount of the binder resin. If the content is 1% by mass or more, the effect can be suitably expressed. Furthermore, if the content is 30% by mass or less, thermal aggregation (blocking) of the toner can be avoided.

(metal fine particles)
The metal fine particles used in the present invention are not particularly limited as long as they are mainly metal-based fine particles. The metal fine particles may be made of a single metal, or the surface of the metal fine particles may be coated with a material other than metal.

Examples of metals constituting the metal fine particles include aluminum, brass, bronze, nickel, stainless steel, zinc, copper, silver, gold, and platinum. Note that in this specification, the metal of the metal fine particles includes an alloy. The metal fine particles may have a core-shell structure formed by metals. The shape of the metal fine particles is not particularly limited, and examples include spherical, spindle-like, needle-like, plate-like, scale-like, confetti-like, and irregular shapes. In the present invention, aluminum fine particles are preferably used.

The particle size of the metal fine particles is preferably 100 to 1000 nm, more preferably 150 to 500 nm, on a volume basis. Note that the volume-based median diameter of the metal fine particles can be measured using a dynamic light scattering particle size measuring device, for example, NANOTRAC WAVE (manufactured by Microtrac Bell Co., Ltd.).

The toner base particles according to the present invention may contain one type of metal fine particles, or may contain two or more types of metal fine particles. The content of metal fine particles in the toner base particles can be adjusted as appropriate depending on the type and shape of the metal fine particles and the characteristics required of the toner. When used for the purpose of imparting glitter to the toner, the amount is preferably 1 to 70 parts by weight, more preferably 5 to 50 parts by weight, based on 100 parts by weight of the binder resin.

Note that the toner of the present invention may contain glitter pigments other than metal fine particles. Specific examples of bright pigments other than metal fine particles include mica coated with titanium oxide, yellow iron oxide, etc.; coated flaky inorganic crystal substrates such as barium sulfate, layered silicate, layered aluminum silicate, etc.; single crystals. Examples include plate-like titanium oxide; basic carbonate; acid oxybismuth chloride; natural guanine; flaky glass powder; metal-deposited flaky glass powder.

(colorant)
The toner base particles according to the present invention may optionally contain a colorant. As the colorant, the following known inorganic or organic colorants can be used depending on the color of the toner. The content of the colorant contained in the toner base particles is preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight, based on 100 parts by weight of the binder resin.

Examples of colorants used in yellow toner include C.I. I. Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, 162, C. I. Pigment Yellow 14, Pigment Yellow 17, Pigment Yellow 74, Pigment Yellow 93, Pigment Yellow 94, Pigment Yellow 138, Pigment Yellow 155, Pigment Yellow 180, Pigment Yellow 185, etc. These can be used alone or in combination of two or more. Among these, especially C. I. Pigment Yellow 74 is preferred.

Examples of colorants used in magenta toner include C.I. I. Solvent Red 1, 49, 52, 58, 63, 111, 122, C. I. Examples include Pigment Red 5, 48:1, 53:1, 57:1, 122, 139, 144, 149, 166, 177, 178, and 222. These can be used alone or in combination of two or more. Among these, C. I. Pigment Red 122 is preferred.

Examples of colorants used in cyan toners include C.I. I. Pigment Blue 15:3 and the like.

Examples of the colorant used in the black toner include carbon black, magnetic material, and titanium black. Examples of carbon black include channel black, furnace black, acetylene black, thermal black, and lamp black. Examples of magnetic materials include ferromagnetic metals such as iron, nickel, and cobalt, alloys containing these ferromagnetic metals, compounds of ferromagnetic metals such as ferrite and magnetite, and compounds that do not contain ferromagnetic metals but can be made ferromagnetic by heat treatment. Examples include the alloys shown below. Examples of alloys that exhibit ferromagnetism upon heat treatment include Heusler alloys such as manganese-copper-aluminum and manganese-copper-tin, and chromium dioxide.

(Release agent)
The toner base particles according to the present invention may contain a release agent if necessary. As the mold release agent, various known waxes can be used.

Examples of the wax include low molecular weight polyethylene wax, low molecular weight polypropylene wax, Fischer-Tropsch wax, microcrystalline wax, hydrocarbon waxes such as paraffin wax, carnauba wax, pentaerythritol behenate, behenyl behenate, and citric acid. Examples include ester waxes such as behenyl acid. These can be used alone or in combination of two or more.

Further, the melting point of the wax is preferably 50 to 95° C. from the viewpoint of ensuring low-temperature fixing properties and releasing properties of the toner. The content ratio of wax as a mold release agent is preferably 2 to 20 parts by weight, more preferably 3 to 18 parts by weight, and still more preferably 4 to 15 parts by weight based on 100 parts by weight of the binder resin. be.

(Charge control agent)
Further, the toner base particles according to the present invention may contain a charge control agent, if necessary.

Various known charge control agents can be used. As the charge control agent, various known positive charge control agents and negative charge control agents that can be dispersed in an aqueous medium can be used. Specific examples include nigrosine dyes, metal salts of naphthenic acid or higher fatty acids, alkoxylated amines, quaternary ammonium salt compounds, azo metal complexes, salicylic acid metal salts, or metal complexes thereof. The content of the charge control agent is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the binder resin.

(Manufacture and form of toner base particles)
The toner base particles according to the present invention can be produced by a known method such as a kneading and pulverization method, a suspension polymerization method, an emulsion aggregation method, a dissolution suspension method, a polyester stretching method, and a dispersion polymerization method. Among these, it is preferable to employ the emulsion aggregation method. According to the emulsion aggregation method, toner base particles having a sharp particle size distribution and highly controlled particle size and toner circularity can be obtained.

In the emulsion aggregation method, a dispersion of fine particles of binder resin (hereinafter also referred to as "fine binder resin particles") dispersed with a surfactant or a dispersion stabilizer is contained in toner base particles. In the present invention, a dispersion of fine metal particles and a dispersion of fine particles of a colorant as an optional component are mixed, and an aggregating agent is added to agglomerate the particles to a desired particle size of toner base particles, and then or This is a method of forming toner base particles by simultaneously performing agglomeration and fusion between fine binder resin particles to control their shape.

An example of a method for manufacturing toner base particles according to the present invention by an emulsion aggregation method will be shown below. The method for producing toner base particles by an emulsion aggregation method includes the following steps (1) to (5).

(1) A step of preparing a dispersion liquid in which fine metal particles are dispersed in an aqueous medium.
(2) A step of preparing a dispersion liquid in which binder resin fine particles containing internal additives as necessary are dispersed in an aqueous medium.
(3) A step of mixing a dispersion of fine metal particles and a dispersion of fine binder resin particles to aggregate, associate, and fuse the metal fine particles and the binder resin fine particles to form toner base particles.
(4) A step of filtering the toner base particles from the dispersion system (aqueous medium) of the toner base particles and removing surfactant and the like.
(5) Drying the toner base particles.

Note that when the toner base particles contain a colorant, in parallel with (1) and (2), a step of preparing a dispersion liquid in which colorant particles are dispersed in an aqueous medium is performed, and (3) In step ), a dispersion of fine metal particles, a dispersion of fine binder resin particles, and a dispersion of colorant particles are mixed.

The dispersion liquid prepared in (1) and (2) of the above manufacturing method may contain a surfactant and a dispersion stabilizer as necessary. The dispersion can be prepared using mechanical energy. Dispersing machines for dispersing are not particularly limited, and include ultrasonic dispersing machines such as low-speed shearing dispersers, high-speed shearing dispersers, friction-type dispersing machines, high-pressure jet dispersing machines, and ultrasonic homogenizers. , high-pressure impact type dispersion machine Ultimizer, etc.

In addition, in the toner base particles according to the present invention, when the binder resin contains an amorphous resin and a crystalline resin, particles of the amorphous resin (hereinafter referred to as "amorphous resin") may be used as a dispersion of the binder resin particles. A dispersion of crystalline resin particles (hereinafter also referred to as "crystalline resin particles") and a dispersion of crystalline resin particles (hereinafter also referred to as "crystalline resin particles") are mixed so that the ratio of amorphous resin particles to crystalline resin particles is higher. A dispersion mixed in the proportions described is used.

The particle size of the binder resin particles used for the toner base particles is preferably within the range of approximately 50 to 300 nm in volume-based median diameter for both amorphous resin particles and crystalline resin particles. The volume-based median diameter of the binder resin particles can be measured using an electrophoretic light scattering photometer, for example, "ELS-800 (manufactured by Otsuka Electronics Co., Ltd.)".

In step (3) of the above manufacturing method, the average particle size and particle size distribution are controlled by slowly agglomerating while balancing the repulsive force on the surface of the fine particles due to pH adjustment and the cohesive force due to the addition of a flocculant made of an electrolyte body. At the same time, the fine particles are fused together by heating and stirring to control the shape, thereby forming toner base particles.

The flocculant is not particularly limited, but those selected from metal salts are preferably used. For example, salts of monovalent metals such as salts of alkali metals such as sodium, potassium, lithium, salts of divalent metals such as calcium, magnesium, manganese, copper, salts of trivalent metals such as iron, aluminum, etc. Specific salts include sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride, zinc chloride, copper sulfate, magnesium sulfate, manganese sulfate, etc. Among these, especially Preferred are salts of divalent metals. If a salt of a divalent metal is used, agglomeration can proceed with a smaller amount. These may be used alone or in combination of two or more.

In (4), toner base particles are solid-liquid separated from the toner base particle dispersion using a solvent such as water. Washing is performed to remove deposits such as surfactant from the filtered cake-like aggregate containing toner base particles. Specific solid-liquid separation and washing methods include centrifugation, vacuum filtration using an aspirator, Nutsche, etc., filtration using a filter press, etc., and are not particularly limited. . At this time, pH adjustment, pulverization, etc. may be performed as appropriate. Such operations may be repeated.

Dryers used in the drying process (5) include ovens, spray dryers, vacuum freeze dryers, vacuum dryers, stationary shelf dryers, mobile shelf dryers, fluidized bed dryers, and rotary dryers. , a stirring dryer, etc., and these are not particularly limited. The moisture content of the dried toner base particles measured by Karl Fischer coulometric titration is preferably 5% by mass or less, more preferably 2% by mass or less.

The toner base particles according to the present invention may have a multilayer structure such as a core-shell structure including the toner base particles as core particles and a shell layer covering the surface of the core particles. The shell layer does not need to cover the entire surface of the core base particle, and the core particle may be partially exposed. The cross section of the core-shell structure can be confirmed using a known observation means such as a transmission electron microscope (TEM) or a scanning probe microscope (SPM).

In the case of a core-shell structure, the core particles and the shell layer can have different properties such as glass transition point, melting point, hardness, etc., and it is possible to design toner base particles depending on the purpose. For example, a shell layer is formed by aggregating and fusing a resin with a relatively high glass transition point (Tg) on the surface of a core particle containing a binder resin and fine metal particles and having a relatively low glass transition point (Tg). can be formed. It is preferable that the shell layer contains an amorphous resin.

Toner base particles having a core-shell structure can be obtained, for example, by the emulsion aggregation method described above. Specifically, toner base particles having a core-shell structure are produced by first agglomerating, associating, and fusing the binder resin particles for the core particles and the metal fine particles to prepare the core particles, and then dispersing the core particles. It can be obtained by adding binder resin particles for the shell layer to a liquid and agglomerating and fusing the binder resin particles for the shell layer on the surface of the core particle to form a shell layer covering the surface of the core particle. can. It is preferable that the optional internal additives be contained in the core particles.

Further, the core particles may be manufactured to have a multilayer structure of two or more layers made of binder resins having different compositions. For example, when producing binder resin particles having a three-layer structure, it is divided into three stages: 1st stage polymerization (formation of inner layer), 2nd stage polymerization (formation of intermediate layer), and 3rd stage polymerization (formation of outer layer). It can be produced by performing a polymerization reaction to synthesize a binder resin. Furthermore, by changing the composition of the polymerizable monomer in each of the first to third stage polymerization reactions, binder resin particles having a three-layer structure having different compositions can be produced. In addition, for example, in any of the first to third stage polymerizations, by carrying out the synthesis reaction of the binder resin in a state containing an appropriate internal additive such as a mold release agent, it is possible to add an appropriate internal additive. It is possible to form binder resin particles containing three layers.

(Particle size of toner base particles)
The volume average particle diameter of the toner base particles according to the present invention is preferably in the range of 4.5 to 8 μm. From the viewpoint of improving image quality, it is preferable that the particle size be smaller, but if the particle size is small, the adhesion of the toner base particles will increase, resulting in poor cleaning performance. If the volume average particle diameter of the toner base particles is within the above range, both the image quality of the output image and the cleanability can be satisfied, and functions such as charging, development, and transfer can also be achieved. Note that it is more preferable from the above point of view that the particle size of the toner base particles is in the range of 5 to 6.2 μm, and dot reproducibility is also improved so that higher quality images can be obtained.

The volume average particle diameter of the toner base particles is determined as the volume-based median diameter (D50% diameter), for example, by using "Multicizer 3" (manufactured by Beckman Coulter) equipped with data processing software "Software V3.51". It can be measured and calculated using a device connected to a computer system (manufactured by Beckman Coulter).

As a measurement procedure, 0.02 g of toner base particles are dispersed in 20 mL of surfactant solution, and after being blended, ultrasonic dispersion is performed for 1 minute to prepare a toner base particle dispersion liquid. As the surfactant solution, for example, a neutral detergent containing a surfactant component diluted ten times with pure water may be used. This toner base particle dispersion liquid is dropped into a beaker of ISOTON II (manufactured by Beckman Coulter) until the measured concentration is 5 to 10%, and the measurement is performed by setting the count of the measuring device to 25,000 particles. Here, the multisizer 3 used has an aperture diameter of 100 μm. The measurement is performed by dividing the range of 2 to 60 μm into 256, calculating the frequency, and obtaining the 50% particle diameter from the one with the larger volume integrated fraction as the volume-based median diameter (D50% diameter), and calculating the toner volume average. Particle size.

(Average circularity of toner base particles)
The average circularity of the toner base particles is preferably within the range of 0.930 to 1.000, and preferably within the range of 0.950 to 0.995, from the viewpoint of improving charging stability and low-temperature fixability. It is more preferable that there be.

If the average circularity is within the above range, individual toner base particles will be less likely to be crushed. As a result, it is possible to suppress contamination of the triboelectric charging member, stabilize the charging property of the toner, and improve the quality of the image formed.

The average circularity of toner base particles can be measured using FPIA-2100 (manufactured by Sysmex). It should be noted that the irregularities that appear on the surface of the toner base particles due to the inclusion of metal fine particles are microscopic irregularities that cannot be detected in particle images using this FPIA-2100, and do not affect the average circularity. I can say that.

Specifically, a measurement sample (toner base particles) is mixed with an aqueous solution containing a surfactant, and an ultrasonic dispersion treatment is performed for 1 minute to disperse the sample. Thereafter, photography is performed using FPIA-2100 (manufactured by Sysmex) under the measurement condition HPF (high magnification imaging) mode at an appropriate density with the number of HPF detections of 3000 to 10000. If the number of HPF detections is within the above range, reproducible measurement values can be obtained. From the captured particle image, calculate the circularity of each toner base particle according to the following formula (2), and calculate the average circularity by adding the circularity of each toner base particle and dividing by the total number of toner base particles. obtain.
Equation (2): Circularity of toner base particles = (perimeter of a circle with the same projected area as the particle image) / (perimeter of the particle projection image)

<External additives>
The toner of the present invention contains fine alumina particles having a number average primary particle size within the range of 8 to 30 nm as an external additive. Hereinafter, alumina fine particles having a number average primary particle size within the range of 8 to 30 nm are also referred to as alumina fine particles (A). The toner of the present invention may contain only alumina fine particles (A) as an external additive, or may contain components other than alumina fine particles (A).

(Alumina fine particles (A))
The alumina fine particles (A) are attached to the surface of the toner base particles as an external additive. The toner base particles have irregularities on the surface, and fine metal particles are present in the convex portions. The alumina fine particles (A) are composed of alumina, and have a number average primary particle size within the range of 8 to 30 nm, so that they are fixed in the recesses of the toner base particles. If the number average primary particle diameter is outside the range, the particles cannot be sufficiently immobilized in the recesses.

The shape of the alumina fine particles (A) is not particularly limited as long as the number average primary particle size measured by the following method is within the range of 8 to 30 nm. Examples of the shape of the alumina fine particles (A) include spherical, spindle-shaped, needle-like, plate-like, scale-like, confetti-like, and irregular shapes, with spherical being preferred.

The number average primary particle size of the alumina fine particles (A) is preferably within the range of 10 to 20 nm, more preferably within the range of 12 to 15 nm. Note that the number average primary particle size of the alumina fine particles (A) refers to the number average primary particle size measured by the following method. Further, the number average primary particle diameters of other external additives to be described later are also the number average primary particle diameters measured by the same method.

(Method for measuring number average primary particle size)
Using a scanning electron microscope (SEM) "JEM-7401F" (manufactured by JEOL), a toner (a toner obtained by externally adding (dispersing) alumina fine particles to toner base particles) magnified 30,000 times. Take a SEM photo. The photograph is observed, and the longest and shortest diameters of each of the 100 alumina particles externally added to the toner base particles are measured, and the intermediate value is defined as the spherical equivalent diameter and the primary particle diameter of each particle. Then, the average of the 100 measured primary particle sizes is defined as the number average primary particle size.

The alumina fine particles (A) do not necessarily need to be composed only of alumina (Al ₂ O ₃ ). The alumina fine particles (A) may contain at least 60% by mass of alumina in the constituent materials of the alumina fine particles (A). The content of alumina in the constituent material of the alumina fine particles (A) is preferably 70% by mass or more, more preferably 80% by mass or more. Components other than alumina contained in the constituent materials of the alumina fine particles (A) include silica, titania, ferrite, and the like.

The method for producing the alumina fine particles (A) is not particularly limited. The alumina fine particles (A) can be produced, for example, by a method of evaporating and burning aluminum trichloride (AlCl ₃ ).

Aluminum trichloride (AlCl ₃ ) is evaporated in an evaporator and the resulting vapor is passed with nitrogen into the mixing chamber of the burner. Here, the gas stream is mixed with hydrogen and air and fed to the flame via a central tube. Additionally, hydrogen is supplied as a jacket-type gas via the outer tube. The gas is combusted in the reaction chamber and cooled in a downstream agglomeration zone to effect agglomeration of the alumina primary particles. At this time, the obtained crude alumina powder is separated from the hydrochloric acid-containing gas produced at the same time, and the crude alumina powder is heat-treated to remove impurities and obtain fine alumina particles.

In order to obtain alumina fine particles (A), in the above method, the reaction conditions such as flame temperature, hydrogen or oxygen supply amount, aluminum trichloride quality, residence time in the flame or length of the coagulation zone.

The alumina fine particles (A) obtained by the above manufacturing method may contain impurities other than alumina, such as iron, in a range of 0.5% by mass or less. Moreover, a commercially available product may be used as the alumina fine particles (A).

The content of the alumina fine particles (A) in the toner of the present invention, that is, the amount of the alumina fine particles (A) attached to the toner base particles, is appropriately selected in consideration of the required performance of the toner. The amount of the alumina fine particles (A) attached is preferably within the range of 0.05 to 2.0 parts by mass based on 100 parts by mass of the toner base particles.

The adhesion amount of the alumina fine particles (A) is more preferably within the range of 0.1 to 1.0 parts by mass, and more preferably within the range of 0.3 to 0.7 parts by mass, based on 100 parts by mass of the toner base particles. preferable. When the amount of the alumina fine particles (A) attached is within the above range, the alumina fine particles (A) are appropriately immobilized in the concave portions on the surface of the toner base particles, and the effects of the present invention can be fully exhibited. If the amount of alumina fine particles (A) attached is too small, there will be many concave portions to which no alumina fine particles (A) are attached, and the effect will likely be insufficient. It is assumed that if the amount of alumina fine particles (A) attached is too large, the alumina fine particles (A) will aggregate, making it difficult to exist at a number average primary particle size suitable for producing effects.

The alumina fine particles (A) may be used as they are, or surface-modified alumina fine particles (A) subjected to surface modification such as hydrophobicization may be used.

There are no particular limitations on the method of surface modification, and for example, in the case of surface modification such as hydrophobization, silicon-containing organic compounds are preferred as the surface modifier. Specifically, alkylsilazane compounds, alkyl alkoxysilane compounds, chlorosilane compounds, silicone oil, silicone varnish, etc. can be used. These surface modifiers may be used alone or in combination of two or more.

Examples of alkylsilazane compounds include hexamethyldisilazane (HMDS), heptamethyldisilazane, octamethylcyclotetrasilazane, and 1,1,3,3-tetramethyldisilazane. , 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 1,3-bis(chloromethyl)tetramethyldisilazane, 1,3-bis(3,3,3-trifluoropropyl) -1,1,3,3-tetramethyldisilazane, 1,3-diphenyltetramethyldisilazane, heptamethyldisilazane, 2,2,4,4,6,6-hexamethylcyclotrisilazane, octamethylcyclo Examples include tetrasilazane, 1,1,3,3-tetramethyldisilazane, 2,4,6-trimethyl-2,4,6-trivinylcyclotrisilazane, and the like. Since the thixotropy of the composition tends to decrease, the organic silazane compound is preferably hexamethyldisilazane, 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 1,3 -bis(chloromethyl)tetramethyldisilazane, 1,3-bis(3,3,3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane, 1,3-diphenyltetramethyldisilazane , heptamethyldisilazane, 2,2,4,4,6,6-hexamethylcyclotrisilazane, octamethylcyclotetrasilazane, 1,1,3,3-tetramethyldisilazane, 2,4,6-trimethyl -2,4,6-trivinylcyclotrisilazane and the like. The organic silazane compound is preferably hexamethyldisilazane because the thixotropy of the composition tends to decrease.

Examples of silicone oils include cyclic compounds, linear or branched organosiloxanes, and more specifically, polydimethylsiloxane (PDMS), octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, Includes tetramethylcyclotetrasiloxane and tetravinyltetramethylcyclotetrasiloxane.

Examples of alkylalkoxysilane compounds include trialkylmonoalkoxysilane compounds with one alkoxy group, dialkyldialkoxysilane compounds with two alkoxy groups, and monoalkyltrialkoxysilane compounds with three alkoxy groups. It will be done. In the present invention, as the alkyl alkoxysilane compound used for surface modification of the alumina fine particles (A), a monoalkyltrialkoxysilane compound is preferable, and a monoalkyltrialkoxysilane compound having a structure represented by the following general formula (1) ( Particularly preferred is the silane compound (hereinafter also referred to as silane compound (1)).

General formula (1): X-Si(OR) ₃
[In formula (1), X represents an alkyl group having 2 to 8 carbon atoms. Each R independently represents a methyl group or an ethyl group. ]

By changing the surface modifier of the alumina fine particles (A), the adhesion between the toner base particles and the alumina fine particles (A) and the cohesion between the alumina fine particles (A) are changed. The use of the silane compound (1) is preferable because it allows the alumina fine particles (A) to be appropriately immobilized in the recesses of the toner base particles. Furthermore, the silane compound (1) contains an alkyl group in its structure and therefore has strong hydrophobicity. This is preferable because it can suppress changes in the electrical properties of alumina due to water adsorption.

The alkyl group represented by X in the silane compound (1) may be linear, branched, or cyclic, or a combination thereof. The number of carbon atoms in X is more preferably within the range of 3 to 7, and even more preferably within the range of 4 to 6. In the silane compound (1), OR is a methoxy group or an ethoxy group. Although the three ORs may be different, it is preferable that they are the same from the viewpoint of ease of manufacture.

As a specific method for surface modification of the alumina fine particles (A), for example, a method of spraying a surface modifier on the alumina fine particles (A) according to the present invention or mixing a vaporized surface modifier and heat-treating the alumina fine particles (A) is possible. Can be mentioned. At this time, water, amine, and other catalysts may be used. Here, this dry surface modification is preferably performed under an inert gas atmosphere such as nitrogen.

In addition, a surface modifier is dissolved in a solvent, and this is added to the alumina fine particles (A) according to the present invention, mixed and dispersed, and then heat treatment is performed as necessary, and further drying treatment is performed to obtain a surface modified material. Alumina fine particles (A) can be obtained. Here, the surface modifier may be added after or simultaneously with mixing and dispersing the alumina fine particles (A) in the solvent.

Here, the degree of surface modification in the alumina fine particles (A) surface-modified with the silicon-containing organic compound, preferably the silane compound (1), can be indicated by the carbon content. That is, the carbon content in the surface-modified alumina fine particles (A) is a characteristic value that correlates with the amount of surface modification. For example, when using the silane compound (1), since the alkyl group contains a carbon atom, when the same surface modifier is used, the higher the carbon content, the higher the amount of surface modification. Further, even if the amount of surface modification is the same, the carbon content increases as the alkyl chain length increases.

The carbon content in the surface-modified alumina fine particles (A) is preferably within the range of 1.0 to 8.0% by mass. The carbon content is more preferably within the range of 1.5 to 4.5% by mass, and even more preferably within the range of 2.5 to 3.5% by mass. It is preferable that the carbon content in the surface-modified alumina fine particles (A) is within the above range, since adhesion to the toner base particles will be appropriate and hydrophobicity of the alumina fine particles (A) can also be ensured.

(Method of measuring carbon content)
The amount of carbon in the sample is determined by burning the sample under an oxygen stream and measuring the total amount of CO and CO ₂ generated by IR (infrared rays) absorbance. The amount of carbon can be measured using a known carbon analyzer, for example, a commercially available carbon analyzer "IR-212 (manufactured by LECO Co. Ltd.)". be.

Specifically, a ceramic crucible is placed in the weighing section of a carbon analyzer, and 1 g of a measurement sample is weighed into the crucible. After weighing the measurement sample, add one spoonful of combustion improver with a spatula. The crucible containing the measurement sample and combustion improver is placed on the ceramic table of the device, and combustion treatment is performed using oxygen as the combustion gas to measure the amount of carbon. The carbon content is expressed as the ratio (percentage) of carbon mass to the total mass of the measurement sample.

In the toner of the present invention, the average adhesion strength (hereinafter also simply referred to as "average adhesion strength") of the alumina fine particles (A) on the particle surface of the toner represented by the following formula (A) is 45 to 85%. It is preferably within the range. The average adhesion strength of the alumina fine particles (A) is more preferably within the range of 50 to 70%, and even more preferably within the range of 55 to 65%.

The above average adhesion strength is an index indicating the characteristics of the toner of the present invention. As described later, the average adhesion strength can also be adjusted by controlling the mixing conditions when externally adding alumina fine particles (A) to the toner base particles. However, the above average adhesive strength value largely depends on the properties of the alumina fine particles (A). That is, the alumina fine particles (A) are attached to the surface of the toner base particles so that the average adhesion strength is preferably 45 to 85%, more preferably 50 to 70%, and even more preferably 55 to 65%. It is preferable to have the property of being able to In order to possess this property, the number average primary particle diameter, surface modification, and amount of adhesion to toner base particles of the alumina fine particles (A) are adjusted as described above.

If the average adhesion strength of the alumina fine particles (A) is too strong, the alumina fine particles (A) will be buried in the toner base particles, the toner fluidity will deteriorate, and the triboelectric charging with the carrier particles described below will not be stable. Furthermore, if the average adhesion strength of the alumina particles (A) is too weak, the alumina particles (A) may move on the toner surface or move to the carrier particle surface even though they are present in the recesses of the toner base particles. . The above range of the average adhesion strength of the alumina fine particles (A) is a range in which these problems are unlikely to occur.

Adhesion strength of alumina fine particles=(Al atom abundance ratio in toner after ultrasonic treatment/Al atom abundance ratio in toner before ultrasonic treatment)×100...Formula (A)
However, the toner after ultrasonic treatment in formula (A) is obtained by moistening 3 g of the toner before ultrasonic treatment as a specimen with 40 g of a 0.2% by mass aqueous solution of polyoxyethylphenyl ether in a 100 mL plastic cup. After applying ultrasonic energy at a current value of 60 μA (50 W) for 3 minutes using an ultrasonic homogenizer, filtration was performed using a filter with an opening of 1 μm, washed with 60 mL of pure water, and dried. This is the later toner.

As the ultrasonic homogenizer, for example, "US-1200" (manufactured by Nippon Seiki Co., Ltd.) can be used. In the US-1200, the current can be adjusted using an ammeter attached to the main unit that indicates vibration indication values.

The Al atom abundance ratio in formula (A) is a value calculated by the following formula (B) based on the peak area of each atom obtained by measuring the surface of the toner particle as a specimen by X-ray electron spectroscopy. be.
(Al/(C+O+Si+Ti+Al))×100 atom%...Formula (B)

Note that the Al atom abundance ratio on the toner particle surface can be measured, for example, by the following method.

Using an X-ray photoelectron spectrometer "K-Alpha" (manufactured by Thermo Fisher Scientific), quantitative analysis of aluminum, titanium, silicon, carbon, and oxygen was performed on 10 mg of the sample (toner) under the following analysis conditions. Using the relative sensitivity factor from each atomic peak area, the elemental concentration is calculated for a range starting from the outermost surface of the toner particle to a depth of 3 nm from the outermost surface. Note that 10 mg of the specimen (toner) is an amount equivalent to 100 or more toner particles.

(Measurement condition)
X-ray: Al monochrome source Acceleration: 12kV, 6mA
Resolution: 50eV
Beam system: 400μm
Pass energy: 50eV
Step size: 0.1eV

(Other external additives)
In addition to the alumina fine particles (A) of the present invention, other external additives may be added to the toner of the present invention for the purpose of improving fluidity and chargeability, as long as they do not impede the effects. Other external additives include known inorganic fine particles and organic fine particles. When inorganic fine particles or organic fine particles are externally added in addition to the alumina fine particles (A), the amount thereof is preferably about 0.1 to 10 parts by mass based on 100 parts by mass of toner base particles.

The external additives used may be one type or two or more types. In particular, it is preferable to use two or more types of external additives having different particle sizes. Different particle sizes have different roles as external additives, and in general, the larger the diameter, the more the spacer effect is exerted, reducing the adhesion between toners, and the smaller the diameter, the easier it is to coat the surface of the toner base particles. It is possible to improve liquidity. Regarding the shape, we use not only spherical external additives, but also acicular ones such as rutile titanium oxide, as well as irregular shapes, spindle shapes, spindle shapes, plate shapes, and scale shapes. be able to.

Examples of the inorganic fine particles include silica fine particles, titanium oxide fine particles, zirconia fine particles, zinc oxide fine particles, chromium oxide fine particles, cerium oxide fine particles, antimony oxide fine particles, tungsten oxide fine particles, tin oxide fine particles, tellurium oxide fine particles, manganese oxide fine particles, and Contains boron oxide fine particles.

Among these, silica fine particles are preferably used. The silica fine particles are preferably silica fine particles manufactured by a sol-gel method. Silica fine particles manufactured by the sol-gel method have a uniform particle size (narrow particle size distribution, that is, monodisperse) compared to fumed silica, which is a common manufacturing method, so it is particularly difficult to use external additives with different particle sizes. It is preferable to use two or more types because the particle size can be easily adjusted.

The number average primary particle diameter of the inorganic fine particles is preferably within the range of 3 to 200 nm, more preferably within the range of 5 to 100 nm. When using two types of different particle sizes, the number average primary particle size is within the range of 5 to 15 nm for small diameter inorganic fine particles, and within the range of 15 to 100 nm for large diameter inorganic fine particles. is preferred. Further, when two types of inorganic fine particles having different particle sizes are used, they are externally added to the toner base particles so that the total amount falls within the above range. The ratio of small-diameter inorganic fine particles to large-diameter inorganic fine particles is not particularly limited, but it is preferably in the range of 5 to 80 parts by mass of small-diameter inorganic fine particles to 100 parts by mass of large-diameter inorganic fine particles.

(Surface modification)
The surface of the inorganic fine particles may be subjected to hydrophobization treatment using a known surface modifier, if necessary. The hydrophobization treatment can suppress adhesion of toner base particles to each other due to water adsorption, which is caused by, for example, hydroxyl groups present on the surface of inorganic fine particles.

The surface modifiers used may be one type or two or more types. Examples of the surface modifier include silane coupling agents, silicone oils, titanate coupling agents, aluminate coupling agents, fatty acids, fatty acid metal salts, esterified products thereof, and rosin acids.

Examples of the silane coupling agent include dimethyldimethoxysilane, hexamethyldisilazane (HMDS), methyltrimethoxysilane, isobutyltrimethoxysilane, and decyltrimethoxysilane.

Examples of the silicone oil include cyclic compounds, linear or branched organosiloxanes, and more specifically, organosiloxane oligomers, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and tetramethyl Includes cyclotetrasiloxane and tetravinyltetramethylcyclotetrasiloxane.

The amount of the surface modifier used in the surface hydrophobization treatment is preferably such that the carbon content of the inorganic fine particles after the hydrophobization treatment is within the range of 0.1 to 10% by mass.

The organic fine particles include spherical organic fine particles having a number average primary particle diameter of about 10 to 2000 nm. Specifically, organic fine particles made of homopolymers such as styrene or methyl methacrylate or copolymers thereof can be used.

Furthermore, a lubricant may be externally added to the toner for the purpose of reducing the frictional force between the photoreceptor and the cleaning blade. When a lubricant is externally added, the amount thereof is preferably about 0.1 to 2.0 parts by mass based on 100 parts by mass of toner base particles.

As the lubricant, known fatty acid metal salts can be used. From the viewpoint of ductility, fatty acid metal salts having a Mohs hardness of 2 or less are preferred, and such fatty acid metal salts are preferably salts of metals selected from zinc, calcium, magnesium, aluminum, and lithium.

Among these, fatty acid zinc, fatty acid calcium, fatty acid lithium or fatty acid magnesium are particularly preferred. Further, as the fatty acid of the fatty acid metal salt, higher fatty acids having 12 or more and 22 or less carbon atoms are preferable. If a fatty acid with a carbon number of 12 or more is used, the generation of free fatty acids can be suppressed, and if the fatty acid has a carbon number of 22 or less, the melting point of the fatty acid metal salt will not become too high and good fixing properties can be obtained. Can be done. As the fatty acid, stearic acid is particularly preferred, and as the fatty acid metal salt used in the present invention, from the viewpoint of spreadability, zinc stearate, calcium stearate, and lithium stearate are preferred, and zinc stearate is more preferred. Two or more of these fatty acid metal salts may be used in combination.

The number average particle diameter of the fatty acid metal salt is preferably in the range of 20 μm or less, particularly preferably 2.0 μm or less.

[Manufacture of toner for developing electrostatic latent images]
The toner of the present invention can be obtained by attaching the external additive in the above amount to the surface of the toner base particles. Specifically, the following method is used.

A mechanical mixing device can be used for the process of externally adding and mixing the external additive to the toner base particles. As the mechanical mixing device, a Henschel mixer, a Nauta mixer, a turbular mixer, etc. can be used. Among these, it is preferable to use a mixing device such as a Henschel mixer that can apply shearing force to the particles to be treated, and perform the mixing treatment by increasing the mixing time or increasing the rotational speed of the stirring blade. In addition, when using multiple types of external additives, either all the external additives are mixed with the toner base particles at once, or the mixture is divided into multiple batches depending on the external additives. You can.

In the above toner manufacturing method, the amount of alumina fine particles (A) used as an external additive depends on the mechanical mixing device and mixing method, such as mixing intensity (peripheral speed of stirring blade, etc.), mixing time, mixing temperature, etc. The degree of crushing and the average adhesion strength to toner base particles can be controlled.

[Two-component developer]
The toner for developing electrostatic latent images of the present invention can be used, for example, as a two-component developer for developing electrostatic latent images, which contains the toner of the present invention and a carrier. The two-component developer can be obtained, for example, by mixing the toner of the present invention and carrier particles described below. The mixing device used for mixing is not particularly limited, and examples thereof include a Nauta mixer, a W cone, a V-type mixer, and the like. The content of toner (toner concentration) in the two-component developer is not particularly limited, but is preferably 4.0 to 8.0% by mass.

(carrier particles)
The carrier particles are made of a magnetic material, and known carrier particles can be used. For example, the carrier particles may be coated carrier particles in which the surface of core particles made of magnetic material is coated with resin, or dispersed carrier particles in which fine magnetic powder is dispersed in resin. can do. The average particle diameter of the carrier particles is generally in the range of 10 to 500 μm, preferably in the range of 30 to 100 μm, as a volume-based median diameter measured in the same manner as the toner base particles. The carrier particles are preferably coated carrier particles from the viewpoint of suppressing adhesion of the carrier particles to the photoreceptor. The coated carrier particles will be explained below.

(core material particles)
The core particles constituting the coated carrier particles are made of a magnetic material, for example, a substance that is strongly magnetized in that direction by a magnetic field. The magnetic materials used may be one type or two or more types. Examples of magnetic materials include metals exhibiting ferromagnetism such as iron, nickel, and cobalt, alloys or compounds containing these metals, and alloys exhibiting ferromagnetism upon heat treatment.

Examples of the metal exhibiting ferromagnetism or a compound containing the same include iron, ferrite represented by the following formula (a), and magnetite represented by the following formula (b). M in formulas (a) and (b) represents one or more monovalent or divalent metals selected from the group of Mn, Fe, Ni, Co, Cu, Mg, Zn, Cd, and Li.
Formula (a): MO・Fe ₂ O ₃
Formula (b ₎ : _MFe2O4

Examples of alloys that exhibit ferromagnetism upon heat treatment include Heusler alloys such as manganese-copper-aluminum and manganese-copper-tin, and chromium dioxide. It is preferable that the core material particles are various types of ferrite. This is because the specific gravity of the coated carrier particles is smaller than the specific gravity of the metal constituting the core particles, so that the impact force of stirring in the developing device can be further reduced.

Further, the magnetization of the core particles constituting the carrier particles is preferably such that the saturation magnetization is within the range of 30 to 75 A·m ² /kg and the residual magnetization is 5.0 A·m ² /kg or less. By using core material particles having such magnetic properties, the carrier particles are prevented from being partially agglomerated, and the two-component developer is uniformly dispersed on the surface of the developer transporting member, so that there is no density unevenness. It becomes possible to form a uniform and high-definition toner image.

(Resin for carrier coating)
As the coating resin constituting the coated carrier particles, known resins used for coating core particles of carrier particles can be used. As the coating resin, a resin having a cycloalkyl group is preferable from the viewpoint of reducing the moisture adsorption of the carrier particles and increasing the adhesion with the core particles of the coating layer.

Examples of cycloalkyl groups include cyclohexyl, cyclopentyl, cyclopropyl, cyclobutyl, cycloheptyl, cyclooctyl, cyclononyl and cyclodecyl. Among these, a cyclohexyl group or a cyclopentyl group is preferred, and a cyclohexyl group is more preferred from the viewpoint of adhesion between the coating layer and core particles, such as ferrite particles.

The coating resin is produced, for example, by polymerizing a polymerizable compound containing a monomer having a cycloalkyl group. As the monomer having a cycloalkyl group, it is preferable to use a cycloalkyl ester of methacrylic acid. The coating resin may be a copolymer of the monomer and a monomer having no cycloalkyl group, such as an alkyl (but not having a cyclic structure) ester of methacrylic acid.

The weight average molecular weight (Mw) of the coating resin is, for example, 10,000 to 800,000, more preferably 100,000 to 750,000, as measured by GPC based on polystyrene. The content of the cycloalkyl group in the coating resin is, for example, 10% by mass to 90% by mass. The content of the cycloalkyl group in the resin can be determined, for example, by pyrolysis-gas chromatography/mass spectrometry (P-GC/MS), ¹ H-NMR, or the like.

The average layer thickness of the coating resin in the carrier particles is preferably within the range of 0.05 to 4.0 μm, more preferably 0.2 μm, from the viewpoint of achieving both carrier durability and low electrical resistance. It is within the range of ~3.0 μm. When the average layer thickness of the coating material is within the above range, charging properties and durability can be set within preferable ranges.

The electrostatic latent image developing toner of the present invention can be applied to known electrophotographic image forming methods and image forming apparatuses without particular limitations. The toner for developing an electrostatic latent image of the present invention can suppress the occurrence of toner scattering even during continuous printing in the toner for developing an electrostatic latent image containing fine metal particles. As a result, the load on the image forming apparatus is reduced, and the occurrence of image forming defects such as fog in printed matter can be suppressed.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various changes can be made.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto. In the examples, "parts" or "%" are used, but unless otherwise specified, "parts by mass" or "% by mass" is expressed.

[1] Preparation of toner base particles (1) Preparation of metal fine particle dispersion 1 A metal fine particle dispersion was prepared using the following materials.
- Aluminum pigment (manufactured by Showa Aluminum Powder Co., Ltd., 2173EA): 100 parts - Anionic surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Neogen R): 1.5 parts - Ion exchange water: 900 parts

After removing the solvent from an aluminum pigment (2173EA) made by turning aluminum fine particles into a paste using a solvent (petroleum-based hydrocarbon), the above anionic surfactant and ion-exchanged water were mixed, and an emulsifying dispersion machine Cavitron (manufactured by Taiheiyo Kiko Co., Ltd.) was used. CR1010) for 1 hour to prepare metal fine particle dispersion 1 (solid content: 10%) in which metal fine particles (aluminum fine particles) were dispersed.

(2) Preparation of binder resin fine particle dispersion (2-1) Preparation of styrene-acrylic resin particle dispersion 1 <1> First stage polymerization Reaction vessel equipped with a stirring device, temperature sensor, cooling pipe, and nitrogen introducing device 4 parts by mass of sodium polyoxyethylene (2) dodecyl ether sulfate and 3000 parts by mass of ion-exchanged water were charged, and the internal temperature was raised to 80°C while stirring at a stirring speed of 230 rpm under a nitrogen stream. After raising the temperature, 10 parts by mass of potassium persulfate dissolved in 200 parts by mass of ion-exchanged water was added to bring the temperature to 75°C, and a monomer mixture having the following composition was added dropwise over 1 hour. A dispersion liquid of resin fine particles [1] was prepared by performing polymerization while heating and stirring at ℃ for 2 hours.

(monomer mixture)
・Styrene 584 parts by mass ・N-Butyl acrylate 160 parts by mass ・Methacrylic acid 56 parts by mass

<2> Second stage polymerization In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device, 2 parts by mass of sodium polyoxyethylene (2) dodecyl ether sulfate was dissolved in 3000 parts by mass of ion-exchanged water. After charging the solution and heating it to 80°C, 42 parts by mass (solid content equivalent) of the above resin fine particles [1] and 70 parts by mass of microcrystalline wax "HNP-0190" (manufactured by Nippon Seiro Co., Ltd.) were added to a mixture with the following composition. A solution dissolved at 80°C is added to the monomer mixture and mixed and dispersed for 1 hour using a mechanical dispersion machine with a circulation path "CLEARMIX" (manufactured by M Techniques) to form emulsified particles (oil). A dispersion containing (drops) was prepared.

(monomer mixture)
・Styrene 239 parts by mass ・N-Butyl acrylate 111 parts by mass ・Methacrylic acid 26 parts by mass ・N-Octyl mercaptan 3 parts by mass

Next, an initiator solution prepared by dissolving 5 parts by mass of potassium persulfate in 100 parts by mass of ion-exchanged water was added to this dispersion, and the system was heated and stirred at 80°C for 1 hour to perform polymerization. A dispersion of resin fine particles [2] was prepared.

<3> Third stage polymerization To the dispersion of the resin fine particles [2] above, a solution of 10 parts by mass of potassium persulfate dissolved in 200 parts by mass of ion-exchanged water was further added, and the mixture was heated at a temperature of 80°C. A monomer mixture having the following composition was added dropwise over 1 hour. After completion of the dropwise addition, polymerization was carried out by heating and stirring for 2 hours, followed by cooling to 28° C. to obtain styrene-acrylic resin particle dispersion 1.

(monomer mixture)
・Styrene 380 parts by mass ・N-Butyl acrylate 132 parts by mass ・Methacrylic acid 39 parts by mass ・N-Octyl mercaptan 6 parts by mass

(2-2) Preparation of crystalline resin particle dispersion 1 <1> Synthesis of crystalline resin particles As a material for the polyester polymerized segment, 220 parts by mass of sebacic acid (molecular weight 202.25), a polyhydric carboxylic acid compound, 298 parts by mass of 1,12-dodecanediol (molecular weight 202.33), a hydrolic alcohol compound, was placed in a reaction vessel equipped with a nitrogen introduction tube, a dehydration tube, a stirrer, and a thermocouple, and heated to 160° C. to dissolve it. Thereafter, 2.5 parts by mass of tin(II) 2-ethylhexanoate and 0.2 parts by mass of gallic acid were added, the temperature was raised to 210°C, and reaction was carried out for 8 hours. The reaction was further carried out at 8.3 kPa for 1 hour to obtain Crystalline Resin 1.

A DSC curve of the obtained crystalline resin 1 was obtained using a differential scanning calorimeter "Diamond DSC" (manufactured by PerkinElmer Co., Ltd.) at a heating rate of 10° C./min. The melting point (Tm) measured by the method of measuring the endothermic peak top temperature was 82.8°C, and the molecular weight measured by GPC "HLC-8120GPC" (manufactured by Tosoh Corporation) showed that Mw in terms of standard styrene was It was 28,000.

<2> Preparation of Crystalline Resin Particle Dispersion 1 The above crystalline resin 1 was dissolved in 100 parts by mass and 400 parts by mass of ethyl acetate. Next, 25 parts by mass of a 5.0% by mass aqueous sodium hydroxide solution was added to prepare a resin solution. This resin solution was put into a container equipped with a stirring device, and while stirring the resin solution, 638 parts by mass of a 0.26 mass % sodium lauryl sulfate aqueous solution was added dropwise and mixed over 30 minutes. During the dropping of the sodium lauryl sulfate aqueous solution, the liquid in the reaction vessel became cloudy, and after dropping the entire amount of the sodium lauryl sulfate aqueous solution, an emulsion in which resin solution particles were uniformly dispersed was prepared. Next, the emulsion was heated to 40°C, and ethyl acetate was removed by distillation under reduced pressure of 150 hPa using a diaphragm vacuum pump "V-700" (manufactured by BUCHI) to remove the ethyl acetate from the crystalline polyester resin. A crystalline resin particle dispersion liquid 1 was obtained.

(3) Agglomeration/fusing step: In a reaction vessel equipped with a stirring device, a temperature sensor, a cooling pipe, and a nitrogen introduction device, 300 parts by mass (in terms of solid content) of the styrene-acrylic resin particle dispersion 1 and a crystalline 60 parts by mass (in terms of solid content) of the resin fine particle dispersion 1, 1100 parts by mass of ion-exchanged water, and 40 parts by mass (in terms of solid content) of the metal particulate dispersion 1 were charged, and the liquid temperature was raised to 30°C. After adjustment, the pH was adjusted to 10 by adding a 5N aqueous sodium hydroxide solution. Next, an aqueous solution in which 60 parts by mass of magnesium chloride was dissolved in 60 parts by mass of ion-exchanged water was added at 30° C. over 10 minutes with stirring. After holding for 3 minutes, the temperature was started to increase, and the system was heated to 85° C. over 60 minutes, and while the temperature was maintained at 85° C., agglomeration was performed to continue the particle growth reaction.

In this state, the particle size of the aggregated particles was measured using "Coulter Multisizer 3" (manufactured by Beckman Coulter), and when the volume-based median diameter reached 6.2 μm, 40 parts by mass of sodium chloride was ionized. An aqueous solution dissolved in 160 parts by mass of exchanged water was added to stop particle growth, and further, as a ripening step, the particles were heated and stirred at a liquid temperature of 80°C for 1 hour to advance the fusion between the particles. A dispersion of toner base particles 1 having an average circularity of 0.97 was prepared.

(4) Washing/drying process The generated dispersion of toner base particles 1 is separated into solid and liquid using a basket type centrifuge “MARKIII model number 60×40+M” (manufactured by Matsumoto Kikai Co., Ltd.), and the wet cake of toner base particles 1 is separated into solid and liquid. was formed. This wet cake was washed with ion-exchanged water at 40°C in the basket centrifuge until the electrical conductivity of the filtrate reached 5 μS/cm, and then transferred to a "Flash Jet Dryer" (manufactured by Seishin Enterprise Co., Ltd.). Toner base particles 1 were prepared by drying until the moisture content became 0.5% by mass.

[2] Preparation of external additives (1) Preparation of alumina fine particles (1-1) Preparation of alumina fine particles A1 320 kg/h of aluminum trichloride (AlCl ₃ ) was evaporated in an evaporator at about 200°C to remove chloride. Steam is passed through the mixing chamber of the burner with nitrogen. Here, the gas stream is mixed with 100 Nm ³ /h of hydrogen and 450 Nm ³ /h of air and fed to the flame via a central tube (7 mm diameter). As a result, the burner temperature is 230° C. and the tube discharge speed is about 35.8 m/s. 0.05 Nm ³ /h of hydrogen are supplied as jacket-type gas via the outer tube. The gas is combusted in the reaction chamber and cooled to about 110° C. in the downstream agglomeration zone.

There, agglomeration of the primary particles of alumina takes place. The aluminum oxide particles obtained are separated in a filter or cyclone from the hydrochloric acid-containing gas produced at the same time, and the adhesive chlorides are removed by treating the powder with moist air at about 500-700°C. In this way, alumina fine particles 1 having a number average primary particle size of 13 nm could be obtained.

The alumina fine particles 1 obtained above were placed in a reaction vessel, and while stirring the powder with a rotary blade under a nitrogen atmosphere, 20 g of isobutyltrimethoxysilane was added as a hydrophobizing surface modifier to 100 g of the alumina fine particles 1 in hexane. A diluted product of 60 g was added, heated and stirred at 200° C. for 120 minutes, and then cooled with cooling water to obtain surface-modified alumina fine particles 1. The obtained alumina fine particles are referred to as alumina fine particles A1.

(1-2) Preparation of alumina fine particles A2 to A17 and alumina fine particles Cf1 to Cf4 By changing the flame temperature in the production of the above alumina fine particles 1, the number average primary particle diameter was 6 nm, 8 nm, 17 nm, 24 nm, respectively. Alumina fine particles 2 to 7 of 30 nm and 32 nm were produced.

Alumina fine particles A2 to A17 and alumina fine particles shown in Table I were prepared by combining alumina fine particles 1 to 7 with the hydrophobizing surface modifier shown below and further producing alumina fine particles A1 in the same manner as producing alumina fine particles A1 except for changing the amount of treatment. Cf1 to Cf4 were produced. Alumina fine particles A1 to A17 are alumina fine particles applicable to the toner of the present invention, and alumina fine particles Cf1 to Cf4 are alumina fine particles for comparative examples.

<Surface modifier; compound (1)>
C2; Ethyltrimethoxysilane C4; Isobutyltrimethoxysilane C8; n-octyltrimethoxysilane

<Surface modifier; silicon-containing organic compound other than compound (1)>
C10; n-decyltrimethoxysilane HMDS; hexamethyldisilazane PDMS; polydimethylsiloxane (molecular weight: 8000)

Table I also shows the carbon content (%) of each alumina fine particle measured by the above method.

[Preparation of toner 1]
To 100 parts by mass of the toner base particles 1 produced as described above, the following three types of fine particles were added as external additives in the following amounts, and Henschel mixer model "FM20C/I" (Nippon Coke Kogyo Co., Ltd.) Co., Ltd.) and stirred for 20 minutes at a rotational speed such that the circumferential speed of the blade tip was 50 m/s to prepare "Toner 1". In addition, the product temperature during external addition mixing was set to be 40°C ± 1°C, and when it reached 41°C, cooling water was poured into the external bath of the Henschel mixer at a flow rate of 5 L/min. When the temperature reached 39° C., the temperature inside the Henschel mixer was controlled by flowing cooling water at a rate of 1 L/min.

(external additive)
・Silica fine particles 1 1.0 parts by mass ・Silica fine particles 2 0.4 parts by mass ・Alumina fine particles A1 0.5 parts by mass

Silica fine particles 1 are silica fine particles having a carbon content of 1.0% by mass, which are obtained by subjecting silica fine particles having a number average primary particle diameter of 20 nm to HMDS treatment. Silica fine particles 2 are silica fine particles having a carbon content of 2.5% by mass, which are obtained by subjecting silica fine particles having a number average primary particle diameter of 8 nm to HMDS treatment.

[Preparation of toners 2 to 38]
Toners 2 to 38 were prepared in the same manner as Toner 1, except that the type of alumina fine particles, the number of parts added, the presence or absence of addition of Silica Fine Particles 1 and Silica Fine Particles 2, and the stirring time were changed as shown in Table II. In Table II, when silica fine particles are added, the amounts of silica fine particles 1 and silica fine particles 2 added are all the same as in the case of toner 1. In the case of "no" addition of silica fine particles, neither silica fine particles 1 nor silica fine particles 2 are added.

[Toner evaluation]
<Average adhesion strength>
For Toners 1 to 38 obtained above, the average adhesion strength of alumina fine particles was measured by the method described above. The results are shown in Table II.

<Preparation of two-component developer>
Two-component developers 1 to 37 were prepared by mixing toners 1 to 38 prepared as described above with carrier 1 prepared as follows at a toner concentration of 6.5% by mass. Evaluation was performed by measuring the amount of toner scattering. The mixture was mixed for 30 minutes using a V-type mixer.

<Preparation of carrier>
(Preparation of carrier core material particles 1)
The raw materials were weighed so as to have MnO: 35 mol%, MgO: 14.5 mol%, Fe ₂ O ₃ : 50 mol% and SrO: 0.5 mol%, mixed with water, and then ground in a wet media mill for 5 hours. A slurry was obtained.

The obtained slurry was dried with a spray dryer to obtain perfectly spherical particles. After adjusting the particle size of the particles, they were heated at 950° C. for 2 hours to perform temporary firing. After pulverizing for 1 hour in a wet ball mill using stainless steel beads with a diameter of 0.3 cm, the mixture was further pulverized for 4 hours using zirconia beads with a diameter of 0.5 cm. PVA (polyvinyl alcohol) was added as a binder in an amount of 0.8% by mass based on the solid content, and then granulated and dried using a spray dryer, and maintained at a temperature of 1350°C for 5 hours in an electric furnace to perform main firing. .

Thereafter, it was crushed, further classified to adjust the particle size, and then low-magnetic products were separated by magnetic separation to obtain carrier core material particles 1. The particle size of carrier core material particles 1 was 35 μm.

(Preparation of core material coating resin 1)
Cyclohexyl methacrylate and methyl methacrylate were added to a 0.3% by mass aqueous solution of sodium benzenesulfonate at a "mass ratio = 5:5" (copolymerization ratio), and 0.5% by mass of the total monomer amount was added. "Core material coating resin 1" was prepared by adding an amount of potassium persulfate to perform emulsion polymerization and drying by spray drying. The weight average molecular weight of the obtained core material coating resin 1 was 500,000.

(Preparation of carrier 1)
100 parts by mass of "Carrier core material particles 1" prepared above as core material particles and 4.5 parts by mass of "Core material coating resin 1" were put into a high-speed stirring mixer equipped with horizontal stirring blades, and the mixture was heated with horizontal rotary blades. After mixing and stirring at 22°C for 15 minutes at a circumferential speed of 8 m/sec, the coating material is applied to the surface of the core particles by mechanical impact force (mechanochemical method) by mixing at 120°C for 50 minutes. was coated to produce "Carrier 1".

<Toner scattering amount measurement>
The amount of toner scattering is measured using a particle counter "KR-12A" (manufactured by RION Co., Ltd.) according to the following procedure. The developing device into which the two-component developer 1 has been charged is set in a drive device that can rotate the developing roller, and the suction port of the particle counter is set at a position 1 cm away from the front end of the developing roller. The particle size measuring range of the particle counter is set to 2 to 10 μm, and the developing roller is rotated at 270 rpm. Measurement with a particle counter was performed by counting for 20 seconds and stopping for 10 seconds, repeated 5 times, and the average value of the 5 times was taken as the amount of scattering.

The above-mentioned scattering amount measurement was performed after filling the developing device with two-component developer 1 and stirring for 1 minute (results are shown as "initial" in Table II). " (manufactured by Konica Minolta), and after printing 50,000 sheets of horizontal bands with a print area ratio of 5% in an environment of 23 ° C and 50% RH (in Table II, as "Durability <NN environment>") After printing 50,000 sheets of horizontal bands with a printing area ratio of 5% in an environment of 30°C and 80% RH (results are shown as "Durability <HH environment>" in Table II), It was carried out three times, and those with 50,000 pieces/L or less under all conditions were considered to have passed.

In the same manner as above, the amount of toner scattering was also measured for two-component developers 2 to 38. The results are shown in Table II.

Table II shows that the toner of the present invention can suppress the occurrence of toner scattering during continuous printing both in normal temperature and humidity environments and in high temperature and high humidity environments.

Claims (5)

A toner for developing an electrostatic latent image, comprising toner base particles containing a binder resin and fine metal particles, and an external additive attached to the surface of the toner base particles,
The metal fine particles contained within the toner base particles include aluminum fine particles having a volume-based median diameter within a range of 150 to 500 nm;
A toner for developing electrostatic latent images, characterized in that the external additive contains alumina fine particles having a number average primary particle size within a range of 8 to 30 nm. The toner for developing electrostatic latent images according to claim 1, wherein the amount of the alumina fine particles attached is within the range of 0.05 to 2.0 parts by mass based on 100 parts by mass of the toner base particles. . 3. The toner for developing electrostatic latent images according to claim 1, wherein the alumina fine particles are surface-modified with a silane compound having a structure represented by the following general formula (1).
General formula (1): X-Si(OR) ₃
[In formula (1), X represents an alkyl group having 2 to 8 carbon atoms. Each R independently represents a methyl group or an ethyl group. ] The toner for developing electrostatic latent images according to claim 3, wherein the carbon content of the surface-modified alumina fine particles is within a range of 1.0 to 8.0% by mass. Any one of claims 1 to 4, wherein the average adhesion strength of the alumina fine particles on the particle surface of the toner represented by the following formula (A) is within a range of 45 to 85%. The toner for developing an electrostatic latent image as described in .
Adhesion strength of alumina fine particles=(Al atom abundance ratio in toner after ultrasonic treatment/Al atom abundance ratio in toner before ultrasonic treatment)×100...Formula (A)
However, the toner after ultrasonic treatment in formula (A) is obtained by moistening 3 g of the toner before ultrasonic treatment as a specimen with 40 g of a 0.2% by mass aqueous solution of polyoxyethylphenyl ether in a 100 mL plastic cup. After applying ultrasonic energy at a current value of 60 μA (50 W) for 3 minutes using an ultrasonic homogenizer, filtration was performed using a filter with an opening of 1 μm, washed with 60 mL of pure water, and dried. This is the later toner.
The Al atom abundance ratio in formula (A) is a value calculated by the following formula (B) based on the peak area of each atom obtained by measuring the surface of the toner particle as a specimen by X-ray electron spectroscopy. be.
(Al/(C+O+Si+Ti+Al))×100 atom%...Formula (B)