JP2016090965A - Toner for electrostatic latent image development - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a toner for electrostatic latent image development that has an excellent heat-resistant storage property, transferability, and cleanability.SOLUTION: A toner for electrostatic latent image development of the present invention contains toner particles including toner base particles. The toner base particles each include a toner core and a shell layer coating the toner core. The shell layer includes a thermosetting component. The toner base particles have an average circularity of 0.965 or more and 0.980 or less. After the toner particles are left in an environment of a temperature of 23°C and a humidity of 50%RH for 24 hours or more, the charge attenuation coefficient of a charge held on the surface of the toner particles is measured to be 0.007 or more and 0.030 or less.SELECTED DRAWING: None

Description

  The present invention relates to an electrostatic image developing toner.

  From the viewpoint of energy saving and downsizing of the image forming apparatus, a toner that can be fixed satisfactorily without heating the fixing roller as much as possible is desired. In general, a binder resin having a low melting point or glass transition point or a release agent having a low melting point is often used for preparing a toner having excellent low-temperature fixability. However, when such toner is stored at a high temperature, there is a problem that toner particles contained in the toner tend to aggregate. When toner particles are aggregated, the charge amount of the aggregated toner particles tends to be lower than that of other non-aggregated toner particles.

  The toner particles contained in the capsule toner have a toner core and a shell layer formed on the surface of the toner core. Patent Document 1 discloses a technique for improving the low-temperature fixability and storage stability of a toner by defining the volume average particle diameter and average circularity of colored resin particles and the average breaking strength of the toner, respectively.

JP 2007-171272 A

  However, with the technology disclosed in Patent Document 1, it is difficult to provide a toner that is excellent in heat-resistant storage stability, transferability, and cleaning properties.

  The present invention has been made in view of the above-described problems, and an object thereof is to improve the heat-resistant storage stability, transferability, and cleaning properties of an electrostatic latent image developing toner.

  The electrostatic latent image developing toner of the present invention contains toner particles including toner base particles. The toner base particles include a toner core and a shell layer that covers the toner core. The shell layer includes a thermosetting component. The toner mother particles have an average circularity of 0.965 or more and 0.980 or less. The charge attenuation coefficient of the charge held on the surface of the toner particles measured after leaving the toner particles in a temperature 23 ° C., humidity 50% RH environment for 24 hours or more is from 0.007 to 0.030.

  According to the present invention, it is possible to provide a toner for developing an electrostatic latent image that is excellent in heat-resistant storage, transferability, and cleaning properties.

  Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. In addition, about the location where description overlaps, although description may be abbreviate | omitted suitably, the summary of invention is not limited.

  The electrostatic latent image developing toner (also simply referred to as toner) according to this embodiment is a powder composed of a large number of toner particles. The toner according to the exemplary embodiment can be used in, for example, an electrophotographic apparatus (image forming apparatus).

  The toner may be used as a one-component developer. The toner may be mixed with a desired carrier and used as a two-component developer.

  In an electrophotographic apparatus, an electrostatic latent image is developed using a developer containing toner. As a result, charged toner adheres to the electrostatic latent image formed on the photoreceptor. Then, after the adhered toner is transferred to the transfer belt, the toner image on the transfer belt is further transferred to a recording medium (for example, paper). Thereafter, the toner is heated to fix the toner on the recording medium. As a result, an image is formed on the recording medium. For example, a full color image can be formed by superposing four color toner images of black, yellow, magenta, and cyan.

The toner according to the exemplary embodiment has the following configurations (1) to (3).
(1) Contains toner particles including toner base particles. The toner base particles include a toner core and a shell layer covering the toner core surface. The shell layer includes a thermosetting component.
(2) The average circularity of the toner base particles is 0.965 or more and 0.980 or less.
(3) The charge attenuation coefficient of the charge held on the surface of the toner particles measured after leaving the toner particles in a 23 ° C., 50% RH environment for 24 hours or more is from 0.007 to 0.030.

  Configuration (1) is useful for achieving both heat-resistant storage stability and low-temperature fixability of the toner. Specifically, it is considered that the heat resistant storage stability of the toner is improved by covering the toner core with the shell layer. Further, the heat resistant storage stability of the toner is improved by including the thermosetting component in the shell layer. In order to further improve the heat resistant storage stability of the toner, 80% by mass or more of the resin component contained in the shell layer is preferably a thermosetting component, and 90% by mass or more of the resin is thermosetting. More preferably, the resin is a thermosetting component.

  The configuration (2) is useful for achieving both toner cleaning properties and transfer properties. Specifically, when the average circularity of the toner base particles is 0.965 or more and 0.980 or less, the toner is efficiently transferred and the slipping of the cleaning blade can be suppressed.

  The configuration (3) is useful for achieving both toner cleaning properties and transfer properties. Specifically, if the charge decay coefficient of the toner particle surface charge measured after leaving the toner particles in a 23 ° C. and 50% RH environment for 24 hours or longer is 0.007 to 0.030, the charge is increased. In addition, occurrence of image defects (for example, toner dropping or fogging) can be suppressed.

  The electrostatic latent image developing toner of the present embodiment (hereinafter also simply referred to as toner) includes toner particles. The toner particles include toner base particles. The toner base particles include a toner core and a shell layer that covers the toner core. The toner core is preferably anionic and the shell layer is preferably cationic. Since the toner core has an anionic property, the material of the cationic shell layer can be attracted to the surface of the toner core when the shell layer is formed. On the surface of the toner core, the reaction of the thermosetting component that is the material of the shell layer adsorbed on the toner core proceeds favorably. For this reason, a shell layer can be formed uniformly without using a dispersant. As will be described later, an external additive may be added to the surface of the toner particles, but in this specification, the toner particles to which no external additive is attached may be referred to as “toner mother particles”. is there.

[Toner core]
The toner core includes a binder resin. The toner core may contain an internal additive (for example, a colorant, a release agent, a charge control agent, or a magnetic powder).

(Binder resin)
In the toner core, the binder resin often occupies most of the components (for example, 85% by mass or more). For this reason, it is considered that the properties of the binder resin greatly affect the properties of the entire toner core. For example, when the binder resin has an ester group, a hydroxyl group, an ether group, an acid group, or a methyl group, the toner core has a strong tendency to become anionic, and the binder resin has an amino group, an amine, or an amide group. If so, the toner core tends to be cationic. In order for the binder resin to have a strong anionic property, the hydroxyl value (OHV value) and the acid value (AV value) of the binder resin are each preferably 10 mgKOH / g or more, and each 20 mgKOH / g or more. Is more preferable.

  The binder resin is preferably a resin having one or more functional groups selected from the group consisting of ester groups, hydroxyl groups, ether groups, acid groups, methyl groups, and carboxyl groups, and resins having hydroxyl groups and / or carboxyl groups. Is more preferable. The binder resin having such a functional group easily reacts with the shell material (for example, methylol melamine) to be chemically bonded. When such a chemical bond occurs, the bond between the toner core and the shell layer becomes strong. Further, as the binder resin, a resin having a functional group containing active hydrogen in the molecule is also preferable.

  The glass transition point (Tg) of the binder resin is preferably equal to or lower than the curing start temperature of the shell material. When a binder resin having such a glass transition point (Tg) is used, it is considered that the toner fixability is unlikely to deteriorate even during high-speed toner fixing.

  The glass transition point (Tg) of the binder resin can be measured using, for example, a differential scanning calorimeter. More specifically, by measuring the endothermic curve of the sample (binder resin) using a differential scanning calorimeter, the glass transition point (Tg) of the binder resin is calculated from the change point of specific heat in the obtained endothermic curve. Can be sought.

  The softening point (Tm) of the binder resin is preferably 100 ° C. or lower, and more preferably 95 ° C. or lower. When the softening point (Tm) of the binder resin is 100 ° C. or less, the toner fixability is hardly lowered even during high-speed toner fixing. In addition, when the softening point (Tm) of the binder resin is 100 ° C. or lower, when the shell layer is formed on the surface of the toner core in the aqueous medium, the toner core is partially softened during the curing reaction of the shell layer. Therefore, the toner core is easily rounded by the surface tension. Note that the softening point (Tm) of the binder resin can be adjusted by combining a plurality of resins having different softening points (Tm).

The softening point (Tm) of the binder resin can be measured using, for example, a Koka flow tester. More specifically, a sample (binder resin) is set in the Koka flow tester, and the binder resin is melted and discharged under predetermined conditions. Then, the S-curve of the binder resin is measured. The softening point (Tm) of the binder resin can be read from the obtained S-shaped curve. In the obtained S-curve, if the maximum stroke value is S ₁ and the low-temperature baseline stroke value is S ₂ , the stroke value in the S-curve is “(S ₁ + S ₂ ) / 2”. The temperature (° C.) at which corresponds to the softening point (Tm) of the measurement sample (binder resin).

  As the binder resin, a thermoplastic resin is preferable. Preferable examples of thermoplastic resins that can be used as the binder resin include styrene resins, acrylic resins, olefin resins (more specifically, polyethylene resins or polypropylene resins), vinyl resins (more specifically, Examples thereof include a vinyl chloride resin, a polyvinyl alcohol resin, a vinyl ether resin, or an N-vinyl resin), a polyester resin, a polyamide resin, a urethane resin, a styrene acrylic resin, or a styrene butadiene resin. Among them, the styrene acrylic resin and the polyester resin are excellent in the dispersibility of the colorant in the toner, the charging property of the toner, and the fixing property of the toner to the recording medium, respectively.

  Hereinafter, a styrene acrylic resin that can be used as a binder resin will be described. The styrene acrylic resin is a copolymer of a styrene monomer and an acrylic monomer.

  Suitable examples of the styrenic monomer include styrene, α-methylstyrene, p-hydroxystyrene, m-hydroxystyrene, vinyltoluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, Or p-ethylstyrene is mentioned.

  Preferable examples of the acrylic monomer include (meth) acrylic acid, (meth) acrylic acid alkyl ester, or (meth) acrylic acid hydroxyalkyl ester. Examples of (meth) acrylic acid alkyl esters include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, and (meth) acrylic acid n. -Butyl, iso-butyl (meth) acrylate, or 2-ethylhexyl (meth) acrylate. Examples of (meth) acrylic acid hydroxyalkyl esters include: 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or (meth) acrylic acid 4 -Hydroxypropyl is mentioned. In some cases, acrylic acid and methacrylic acid are collectively referred to as “(meth) acrylic acid”.

  When preparing a styrene acrylic resin, a hydroxyl group is introduced into the styrene acrylic resin by using a monomer having a hydroxyl group (for example, p-hydroxystyrene, m-hydroxystyrene, or (meth) acrylic acid hydroxyalkyl ester). it can. Moreover, the hydroxyl value of the styrene acrylic resin obtained can be adjusted by adjusting the usage-amount of the monomer which has a hydroxyl group.

  When preparing the styrene acrylic resin, a carboxyl group can be introduced into the styrene acrylic resin by using (meth) acrylic acid (monomer). Moreover, the acid value of the styrene acrylic resin obtained can be adjusted by adjusting the usage-amount of (meth) acrylic acid.

  When the binder resin is a styrene acrylic resin, the number average molecular weight (Mn) of the styrene acrylic resin is preferably 2000 or more and 3000 or less in order to achieve both the strength of the toner core and the toner fixing property. The molecular weight distribution of the styrene acrylic resin (ratio Mw / Mn of the mass average molecular weight (Mw) to the number average molecular weight (Mn)) is preferably 10 or more and 20 or less. Gel permeation chromatography can be used to measure Mn and Mw of the styrene acrylic resin.

  Hereinafter, the polyester resin that can be used as the binder resin will be described. The polyester resin is obtained by polycondensation or copolycondensation of a divalent or trivalent or higher alcohol and a divalent or trivalent or higher carboxylic acid.

  Examples of dihydric alcohols that can be used to prepare the polyester resin include diols or bisphenols.

  Suitable examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5- Examples include pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol.

  Preferable examples of bisphenols include bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, or polyoxypropylenated bisphenol A.

  Suitable examples of trihydric or higher alcohols that can be used to prepare the polyester resin include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, Tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, Examples include trimethylolpropane or 1,3,5-trihydroxymethylbenzene.

  Suitable examples of divalent carboxylic acids that can be used to prepare the polyester resin include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, Adipic acid, sebacic acid, azelaic acid, malonic acid, succinic acid, or alkyl succinic acid or alkenyl succinic acid (more specifically, n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid, isododecyl succinic acid, or isododecenyl succinic acid).

  Preferable examples of the trivalent or higher carboxylic acid that can be used for preparing the polyester resin include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2 , 5,7-Naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl- Examples include 2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, or empole trimer acid.

  The divalent or trivalent or higher carboxylic acid may be used as an ester-forming derivative (for example, acid halide, acid anhydride, or lower alkyl ester). Here, “lower alkyl” means an alkyl group having 1 to 6 carbon atoms.

  When preparing the polyester resin, the acid value and hydroxyl value of the polyester resin can be adjusted by changing the amount of alcohol used and the amount of carboxylic acid used. When the molecular weight of the polyester resin is increased, the acid value and hydroxyl value of the polyester resin tend to decrease.

  When the binder resin is a polyester resin, the number average molecular weight (Mn) of the polyester resin is preferably 1000 or more and 2000 or less in order to achieve both the strength of the toner core and the fixing property of the toner. The molecular weight distribution of the polyester resin (the ratio Mw / Mn of the mass average molecular weight (Mw) to the number average molecular weight (Mn)) is preferably 9 or more and 21 or less. Gel permeation chromatography can be used for the measurement of Mn and Mw of the polyester resin.

(Coloring agent)
The toner core may contain a colorant. As the colorant, a known pigment or dye can be used according to the color of the toner. The amount of the colorant to be used is preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the binder resin.

  The toner core may contain a black colorant. An example of a black colorant is carbon black. The black colorant may be a colorant that is toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

  The toner core may contain a color colorant such as a yellow colorant, a magenta colorant, or a cyan colorant.

  Examples of yellow colorants include condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, or allylamide compounds. Suitable examples of yellow colorants include C.I. I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155 168, 174, 175, 176, 180, 181, 191 or 194), Neftol Yellow S, Hansa Yellow G, or C.I. I. Bat yellow is mentioned.

  Examples of magenta colorants include condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, or perylene compounds. Suitable examples of magenta colorants include C.I. I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81: 1, 122, 144, 146, 150, 166, 169, 177 184, 185, 202, 206, 220, 221 or 254).

  Examples of cyan colorants include copper phthalocyanine compounds, copper phthalocyanine derivatives, anthraquinone compounds, or basic dye lake compounds. Suitable examples of cyan colorants include C.I. I. Pigment blue (1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62, or 66), phthalocyanine blue, C.I. I. Bat Blue, or C.I. I. Acid blue.

(Release agent)
The toner core may contain a release agent. The release agent is used, for example, for the purpose of improving the fixing property or offset resistance of the toner. In order to increase the anionicity of the toner core, it is preferable to produce the toner core using an anionic wax. In order to improve the fixing property or offset resistance of the toner, the amount of the release agent used is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin. More preferably, it is 20 parts by mass or less.

  Suitable examples of the release agent include aliphatic hydrocarbon waxes (for example, low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, or Fischer-Tropsch wax), aliphatic Oxides of hydrocarbon wax (eg, oxidized polyethylene wax or block copolymer of oxidized polyethylene wax), plant wax (eg, candelilla wax, carnauba wax, wood wax, jojoba wax, or rice wax), animal Waxes (eg, beeswax, lanolin, or whale wax), mineral waxes (eg, ozokerite, ceresin, or petrolatum), waxes based on fatty acid esters (eg, montanate waxes) The castor wax), or wax deoxidizing part or all of fatty acid esters (e.g., deoxidized carnauba wax) and the like.

  In order to improve the compatibility between the binder resin and the release agent, a compatibilizing agent may be added to the toner core.

(Charge control agent)
The toner core may contain a charge control agent. The charge control agent is used, for example, for the purpose of improving the charging stability or charging rising property of the toner. Further, since the toner core contains a negatively chargeable charge control agent, the anionicity of the toner core is enhanced. The charge rising characteristic of the toner is an index as to whether or not the toner can be charged to a predetermined charge level in a short time.

(Magnetic powder)
The toner core may contain magnetic powder. Examples of magnetic powder include iron (more specifically, ferrite or magnetite), a ferromagnetic metal (more specifically, cobalt or nickel), a compound containing iron and / or a ferromagnetic metal (more specifically, Is an alloy), a ferromagnetic alloy that has been subjected to a ferromagnetization treatment (for example, heat treatment), or chromium dioxide.

  In order to suppress elution of metal ions (for example, iron ions) from the magnetic powder, it is preferable to surface-treat the magnetic powder. When a shell layer is formed on the surface of the toner core under acidic conditions, if the metal ions are eluted on the surface of the toner core, the toner cores are easily fixed to each other. By suppressing the elution of metal ions from the magnetic powder, sticking between the toner cores can be suppressed.

[Shell layer]
The shell layer contains a thermosetting component. The shell layer preferably contains a thermosetting component and a thermoplastic component. In the shell layer, for example, a thermoplastic component is crosslinked with a thermosetting component. Such a shell layer is considered to have both moderate flexibility based on the thermoplastic component and moderate mechanical strength based on the three-dimensional crosslinked structure formed by the thermosetting component. For this reason, a toner composed of toner particles having such a shell layer is excellent in both heat storage stability and low-temperature fixability. Specifically, the shell layer is not easily destroyed during storage or transportation. On the other hand, at the time of fixing, the shell layer is easily broken by applying temperature and pressure, and the softening or melting of the toner core tends to proceed rapidly. For this reason, it is considered that the toner can be fixed on the recording medium at a low temperature.

  The thermoplastic component includes a component that has been modified to a degree that does not significantly change the structure or properties of the matrix of the thermoplastic component (such as introduction of a functional group, oxidation, reduction, or atom replacement). In addition, the thermosetting component includes a component that has been modified to a degree that does not significantly change the structure or properties of the base of the thermosetting component (such as introduction of a functional group, oxidation, reduction, or atom replacement). .

  When the shell layer contains a thermoplastic component and a thermosetting component, a shell layer having a uniform thickness is easily formed on the surface of the toner core. In addition, since the thermosetting component is strong and easily positively charged, when the shell layer is composed of only the thermosetting component, the shell layer may be excessively strongly positively charged. By including a thermoplastic component in the shell layer in addition to the thermosetting component, the charge amount of the toner can be easily adjusted to a desired range. The shell layer may contain a charge control agent (for example, a positively chargeable charge control agent).

  In order to suppress dissolution or elution of the toner core during the formation of the shell layer, it is preferable to form the shell layer in an aqueous medium. For this reason, it is preferable that the shell material has water solubility.

The thermoplastic component has a functional group (for example, a hydroxyl group, a carboxyl group, an amino group, a carbodiimide group, an oxazoline group, or a glycidyl group) that easily reacts with a functional group (for example, a methylol group or an amino group) of the thermosetting component. It is preferable. The amino group may be contained in the thermoplastic component as a carbamoyl group (—CONH ₂ ).

  As the thermoplastic resin, a water-soluble resin is preferable, and a water-soluble resin containing a component having a polar functional group (for example, glycol, carboxylic acid, or maleic acid) is particularly preferable. A thermoplastic resin having a polar functional group has high reactivity. Specific examples of the water-soluble thermoplastic resin include polyvinyl alcohol resin, polyvinyl pyrrolidone, carboxymethyl cellulose (or a derivative thereof), sodium polyacrylate, polyacrylamide, polyethyleneimine, or polyethylene oxide.

  The thermoplastic component preferably includes an acrylic component, and more preferably includes a reactive acrylate. Since the thermoplastic component including the acrylic component is likely to react with the thermosetting component, it is considered that the film quality of the shell layer can be improved. It is particularly preferred that the thermoplastic component comprises 2HEMA (2-hydroxyethyl methacrylate).

  Specific examples of the thermoplastic resin include acrylic resins, styrene acrylic copolymer resins, silicone-acrylic graft copolymers, urethane resins, polyester resins, and ethylene vinyl alcohol copolymers. As the thermoplastic resin, an acrylic resin, a styrene acrylic copolymer resin, or a silicone-acrylic graft copolymer is preferable, and an acrylic resin is more preferable.

  Examples of thermoplastic components contained in the shell layer include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, or n-butyl (meth) acrylate (meta (Meth) acrylic acid aryl esters such as phenyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2- (meth) acrylic acid 2- Hydroxypropyl or (meth) acrylic acid hydroxyalkyl esters such as 4-hydroxybutyl (meth) acrylate; (meth) acrylamide; ethylene oxide adducts of (meth) acrylic acid; methyl ether, ethyl ether, n-propyl ether Or (meth) acrylic acid, such as n-butyl ether Alkyl ethers of ethylene oxide adducts of ester thereof.

  Preferable examples of the thermosetting resin include melamine resin, urea resin, sulfonamide resin, glyoxal resin, guanamine resin, aniline resin, polyimide resin, or derivatives of these resins. The polyimide resin has a nitrogen element in the molecular skeleton. For this reason, the shell layer containing the unit derived from the monomer or prepolymer of the polyimide resin tends to have strong cationic properties. Examples of the polyimide resin include a maleimide polymer or a bismaleimide polymer (more specifically, an amino bismaleimide polymer or a bismaleimide triazine polymer).

  As the thermosetting resin, a resin (hereinafter referred to as an aminoaldehyde resin) produced by polycondensation of a compound containing an amino group and an aldehyde (for example, formaldehyde) is particularly preferable. The melamine resin is a polycondensate of melamine and formaldehyde. Urea resin is a polycondensate of urea and formaldehyde. Glyoxal resin is a polycondensation product of formaldehyde and a reaction product of glyoxal and urea.

  By including a nitrogen element in the thermosetting component, the cross-linking curing function of the thermosetting component can be improved. In order to enhance the reactivity of the thermosetting component, the melamine resin-based thermosetting component is 40% by mass to 55% by mass, and the urea resin-based thermosetting component is about 40% by mass. In the thermosetting component, it is preferable to adjust the content of nitrogen element to about 15% by mass.

  Examples of the thermosetting component contained in the shell layer include methylol melamine, benzoguanamine, acetoguanamine, spiroguanamine, or dimethylol dihydroxyethylene urea (DMDHEU).

  The thickness of the shell layer is preferably 15 nm or less, and more preferably 1 nm or more and 10 nm or less. If the thickness of the shell layer is 15 nm or less, it is likely that the shell layer is easily broken, and the toner can be fixed to the recording medium at a low temperature. Furthermore, when the thickness of the shell layer is 15 nm or less, it is considered that an excessively strong charging property of the shell layer is suppressed, and an image is easily formed properly. On the other hand, when the thickness of the shell layer is 1 nm or more, the shell layer is considered to have sufficient strength. For this reason, it is considered that when an impact (for example, an impact during transportation) is applied to the toner, the shell layer is not easily broken, and the storage stability of the toner is improved. The thickness of the shell layer can be measured by analyzing a cross-sectional TEM image of the toner particles using commercially available image analysis software.

  The shell layer may have a fracture location (a site with weak mechanical strength). The broken portion can be formed by causing a defect or the like locally in the shell layer. By providing the broken portion in the shell layer, the shell layer can be easily broken. As a result, the toner can be fixed on the recording medium at a low temperature. The number of destruction points is arbitrary.

  The average circularity of the toner base particles is 0.965 or more and 0.980 or less. If the average circularity of the toner base particles is 0.965 or more, the toner is efficiently transferred to the recording medium. When the average circularity of the toner base particles is 0.980 or less, the toner particles do not pass through the cleaning blade, and the toner cleaning property is improved.

  The average circularity of the toner base particles can be measured by a commonly used method. For example, by using a flow type particle image analyzer, the circularity of each of 1000 to 5000 toner particles contained in the toner is measured, and the average circularity can be calculated from the measured circularity.

  The average circularity of the toner base particles tends to be influenced by the polymerization time when the shell layer is formed. Specifically, if the polymerization time during the formation of the shell layer is long, the average circularity tends to increase. On the contrary, if the polymerization time at the time of forming the shell layer is short, the average circularity tends to be small.

[External additive]
An external additive may be attached to the surface of the toner base particles. The external additive is used, for example, to improve the fluidity or handleability of the toner. In order to improve the fluidity or handleability of the toner, the amount of the external additive used is preferably 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the toner base particles. In order to improve the fluidity or handleability of the toner, the particle diameter of the external additive is preferably 0.01 μm or more and 1.0 μm or less.

  Preferable examples of the external additive include metal oxides (more specifically, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, or barium titanate), or silica.

  The charge decay coefficient of the charge held on the surface of the toner particles according to the exemplary embodiment is 0.007 or more and 0.030 or less when the toner particles are measured after being left in a temperature 23 ° C., humidity 50% RH environment for 24 hours or more. , Preferably 0.011 or more and 0.021 or less. The charge decay constant of the toner particles can be measured using an electrostatic diffusivity measuring device.

  Hereinafter, a method for calculating the charge decay constant of the toner particles will be described in detail. The toner is put into the measurement cell, and the sample is filled in the recess of the cell. The filling amount of the sample is 0.02 g or more and 0.10 g or less.

Subsequently, the measurement cell filled with the sample is allowed to stand for 24 hours or more in an environment of a temperature of 23 ° C. and a humidity of 50% RH or less. Subsequently, the grounded measurement cell is placed in the electrostatic diffusivity measuring apparatus, and ions are supplied to the sample by corona discharge to charge the sample. And after 0.5 second or more and 1.0 second or less have passed after completion | finish of corona discharge, the surface potential of a sample is measured continuously. Based on the measured surface potential and the formula “V = V ₀ exp (α√t)”, the charge decay constant α is calculated. In the formula, V represents the surface potential [V], V ₀ represents the initial surface potential [V], and t represents the decay time [second].

  A toner having a charge attenuation coefficient of 0.007 or more and 0.030 or less is suitably used for a tandem electrophotographic image forming apparatus. The tandem electrophotographic image forming apparatus includes four transfer units including a photosensitive drum and a transfer roller. The recording medium or intermediate transfer belt is conveyed in the order in which the recording medium or intermediate transfer belt is transferred from the upstream where the recording medium or intermediate transfer belt is transferred first to the downstream where the recording medium or intermediate transfer belt is transferred last. . In the transfer portion, the photosensitive drum and the transfer roller that are in contact with the intermediate transfer belt are charged. When a color image is formed by a tandem electrophotographic image forming apparatus, the most upstream toner tends to be excessively charged under the influence of the photosensitive drum and the transfer roller. If the toner has a charge decay coefficient of 0.007 or more and 0.030 or less, the charge of the toner is moderately attenuated and the toner charge-up is suppressed.

  If the toner cleaning property is not good, the scattered toner in the developing device may accumulate around the blade that regulates the amount of developer carried on the developer carrying member. When the accumulated toner aggregates and adheres to the developing roller, the toner drops and image formation failure occurs.

  The charge decay coefficient tends to be influenced by the content of the thermosetting resin. Specifically, the more the thermosetting resin, the greater the charge decay coefficient. On the contrary, if the thermosetting resin is small, the charge decay coefficient tends to be small.

  The charge decay coefficient tends to be influenced by the shell layer curing temperature. Specifically, the charge decay coefficient tends to increase as the shell layer curing temperature increases. On the contrary, when the shell layer curing temperature is low, the charge decay coefficient tends to be small.

[Career]
The two-component developer may be prepared by mixing the toner according to the exemplary embodiment and the developer carrier. As the developer carrier, for example, a magnetic carrier having a carrier core and a resin layer covering the carrier core can be suitably used. In order to produce a magnetic carrier, the carrier core may be formed of a magnetic material, or magnetic particles may be dispersed in the resin layer. In order to suppress toner scattering and form a high-quality image, the toner content in the two-component developer is preferably 8% by mass or more and 15% by mass or less.

  Next, an example of a toner manufacturing method according to the present embodiment will be described. First, a toner core is prepared. Subsequently, the toner core and the shell material are put in the liquid. At this time, it is preferable to dissolve the shell material in the liquid by, for example, stirring the liquid. Subsequently, a shell layer is formed on the surface of the toner core in the liquid (the shell layer is cured). The shell layer is preferably formed in an aqueous medium (for example, water, methanol, or ethanol). In order to form a shell layer containing a melamine resin or a urea resin, a toner core is placed in a solvent (for example, water, methanol, or ethanol) in which a methylolated product is dissolved, and the melamine resin or urea is formed on the surface of the toner core. It is preferable to form a resin film.

  Hereinafter, the toner manufacturing method will be further described based on a more specific example. For example, ion exchange water is prepared as the liquid. Subsequently, the pH of the solution is adjusted using, for example, hydrochloric acid. Subsequently, the shell material is added to the liquid. Thereby, the shell material is dissolved in the liquid, and a solution of the shell material is obtained. The appropriate addition amount of the shell material can be calculated based on the specific surface area of the toner core.

  Subsequently, the toner core is added to the obtained shell material solution. In order to uniformly adhere the shell material to the surface of the toner core, it is preferable to highly disperse the toner core in a solution of the shell material.

  Subsequently, while stirring the solution, the temperature of the solution is set at a predetermined rate (for example, a rate selected from 0.1 ° C./min to 3 ° C./min) at a predetermined shell layer curing temperature (for example, 50 ° C. to 90 ° C. The temperature of the solution is raised to the shell layer curing temperature for a predetermined time (for example, a time selected from 30 minutes to 3 hours) while stirring the solution. As a result, the shell material adheres to the surface of the toner core, and the attached material is cured by a polymerization reaction. As a result, a dispersion of toner base particles is obtained.

  When the shell material is reacted at a high temperature, the shell layer tends to become hard. When the shell layer is substantially composed of a melamine resin and / or a urea resin, the shell layer curing temperature is preferably 40 ° C. or higher and 90 ° C. or lower, and more preferably 55 ° C. or higher and 80 ° C. or lower. preferable. When the liquid temperature at the time of curing the shell layer is increased, the deformation of the toner core is promoted, and the shape of the toner base particles tends to approach a true sphere. It is desirable to adjust the liquid temperature when the shell layer is cured so that the toner base particles have a desired shape. The molecular weight of the shell layer can also be controlled based on the liquid temperature during shell layer curing.

  After the shell layer is cured as described above, the dispersion of toner base particles is neutralized using, for example, sodium hydroxide. Subsequently, the liquid is cooled. Subsequently, the liquid is filtered. As a result, the toner base particles are separated from the liquid (solid-liquid separation). Subsequently, the obtained toner base particles are washed. Subsequently, the washed toner base particles are dried. Thereafter, an external additive is attached to the surface of the toner base particles as necessary. Thereby, a toner having a large number of toner particles is completed.

  The toner manufacturing method can be arbitrarily changed according to the required configuration or characteristics of the toner. For example, a step of adding the toner core into the solvent may be performed before the step of dissolving the shell material in the solvent. The method for forming the shell layer is arbitrary. For example, the shell layer may be formed using any of an in-situ polymerization method, a submerged cured coating method, and a coacervation method. Further, various processes may be omitted depending on the target toner. When the external additive is not attached to the surface of the toner base particles (the step of external addition is omitted), the toner base particles correspond to the toner particles. In order to produce the toner efficiently, it is preferable to form a large number of toner particles simultaneously.

  A two-component developer can be produced by stirring the produced toner and developer carrier using a mixing device.

(Preparation of aqueous thermoplastic resin solution)
A 1000 mL reactor equipped with a stirrer, a cooling tube, and a temperature sensor was charged with 450 mL of distilled water and 2.0 g of dodecyl ammonium chloride, and the temperature was raised to 80 ° C. while stirring in a nitrogen stream. Thereafter, 120 g of a 1% by mass aqueous potassium persulfate solution was added thereto. Next, a monomer mixed liquid of 140 g of styrene, 30 g of methyl methacrylate, and 3.6 g of n-octyl mercaptan was added over 1.5 hours. Hold for 2 hours to complete the polymerization. After completion of the polymerization reaction, the contents were cooled to room temperature, and distilled water was added to obtain an aqueous thermoplastic resin solution (solid content concentration 8% by mass). The average particle size was 50 nm.

Example 1
(Toner core manufacturing process)
For 100 parts by mass of polyester resin A (hydroxyl value (OHV value) = 20 mgKOH / g, acid value (AV value) = 40 mgKOH / g, softening point (Tm) = 90 ° C., glass transition point (Tg) = 49 ° C.) , 5 parts by mass of a colorant (phthalocyanine pigment 15: 3 type, “CI Pigment Blue” manufactured by Clariant Japan Co., Ltd.), 5 parts by mass of a release agent (ester wax, “WEP-5” manufactured by Nippon Oil & Fats Co., Ltd.) And mixed at 2400 rpm using an FM mixer (Nihon Coke Kogyo Co., Ltd.). Chips obtained by kneading the obtained mixture with a twin screw extruder (“PCM-30” manufactured by Ikegai Co., Ltd.) were pulverized with a mechanical pulverizer (“Turbo Mill T250” manufactured by Freund Turbo). Thereafter, the toner was classified by a classifier (“Elbow Jet EJ-LABO type” manufactured by Nippon Steel Mining Co., Ltd.) to obtain a toner. The average circularity of this toner was 0.93. The obtained toner core had a glass transition point (Tg) of 51 ° C. and a softening point (Tm) of 91 ° C. Further, when the charge amount of the toner core was measured using a standard carrier N-01, the charge amount of the toner core was −20 μC / g. Furthermore, the data potential of the toner core at pH 4 was -15 mV, indicating a clear anionic property.

(Shell layer forming process)
A 1-liter three-necked flask was set in a 30 ° C. water bath, and 300 mL of ion-exchanged water was adjusted to pH 4 with hydrochloric acid. 2 mL of an aqueous solution of a hexamethylol melamine initial polymer (“Milben (registered trademark) Resin SM-607” manufactured by Showa Denko KK, solid content concentration 80% by mass) was added to this solution and dissolved so that a 6 nm film was formed. . To this aqueous solution, 300 g of the toner core obtained in the toner core preparation step was added and stirred sufficiently. Further, 300 mL of ion-exchanged water was added, the temperature was increased at a rate of 1 ° C./min with stirring, and the temperature was maintained at 70 ° C. for 2 hours. Thereafter, it was neutralized to pH 7, filtered, washed and dried to obtain toner mother particles.

(External addition process)
After the drying, the toner base particles were externally added. Specifically, 100 parts by mass of toner base particles and 0.5 parts by mass of dry silica (“AEROSIL (registered trademark) 200” manufactured by Nippon Aerosil Co., Ltd.) as an external additive are mixed with FM mixer (“FM manufactured by Nippon Coke Industries, Ltd.”). -10B ") for 5 minutes at a rotational speed of 3500 rpm, dry silica was adhered to the surface of the toner base particles. Thereafter, the obtained toner was sieved using a sieve of 200 mesh (aperture 75 μm). As a result, a toner containing a large number of toner particles was produced.

Example 2
In the shell layer forming step, 20 mL of an aqueous thermoplastic resin solution is further added when an aqueous solution of hexamethylol melamine initial polymer (“Milben (registered trademark) Resin SM-607” manufactured by Showa Denko KK, solid content concentration 80 mass%) is added. A toner of Example 2 was obtained in the same manner as the toner of Example 1 except that.

Example 3
In the shell layer forming step, the addition amount of the aqueous solution of hexamethylolmelamine initial polymer ("Milben (registered trademark) Resin SM-607" manufactured by Showa Denko KK, solid content concentration 80% by mass) was changed from 2 mL to 3 mL. In the same manner as in the toner of Example 1, the toner of Example 3 was obtained.

Example 4
In the shell layer forming step, a toner of Example 4 was obtained in the same manner as the toner of Example 3 except that the holding at 70 ° C. for 2 hours was changed to holding at 70 ° C. for 1 hour.

Example 5
In the shell layer forming step, the amount of hexamethylolmelamine initial polymer aqueous solution ("Milben (registered trademark) resin SM-607" manufactured by Showa Denko KK, solid content concentration 80 mass%) was changed from 2 mL to 4 mL, A toner of Example 5 was obtained in the same manner as the toner of Example 1, except that the holding at 70 ° C. for 2 hours was changed to holding at 70 ° C. for 1 hour.

Example 6
In the shell layer forming step, the toner of Example 6 was obtained in the same manner as the toner of Example 1, except that the holding at 70 ° C. for 2 hours was changed to holding at 65 ° C. for 2 hours.

Example 7
A toner of Example 7 was obtained in the same manner as the toner of Example 1 except that in the shell layer forming step, the toner was changed from holding at 70 ° C. for 2 hours to holding at 60 ° C. for 2 hours.

Example 8
A toner of Example 8 was obtained in the same manner as the toner of Example 5, except that in the shell layer forming step, the case of holding at 70 ° C. for 1 hour was changed to holding at 75 ° C. for 1 hour.

Example 9
A toner of Example 9 was obtained in the same manner as the toner of Example 5, except that in the shell layer forming step, the condition of holding at 70 ° C. for 1 hour was changed to holding at 80 ° C. for 1 hour.

Comparative Example 1
In the shell layer forming step, the amount of hexamethylolmelamine initial polymer aqueous solution ("Milben (registered trademark) resin SM-607" manufactured by Showa Denko KK, solid content concentration 80 mass%) was changed from 2 mL to 6 mL, A toner of Comparative Example 1 was obtained in the same manner as the toner of Example 1 except that the holding at 70 ° C. for 2 hours was changed to holding at 70 ° C. for 4 hours.

Comparative Example 2
In the shell layer forming step, the toner of Comparative Example 2 was obtained in the same manner as the toner of Example 1 except that the holding at 70 ° C. for 2 hours was changed to holding at 58 ° C. for 4 hours.

Comparative Example 3
In the shell layer forming step, the toner of Comparative Example 3 was obtained in the same manner as the toner of Example 5 except that the holding at 70 ° C. for 2 hours was changed to holding at 80 ° C. for 2 hours.

Comparative Example 4
A toner of Comparative Example 3 was obtained in the same manner as the toner of Example 1 except that the shell layer was not formed.

Comparative Example 5
In the shell layer forming step, an aqueous thermoplastic resin solution was added without adding an aqueous solution of hexamethylolmelamine initial polymer ("Milben (registered trademark) Resin SM-607" manufactured by Showa Denko KK, solid concentration 80 mass%). A toner of Comparative Example 5 was obtained in the same manner as the toner of Example 1 except that 20 mL was added.

  The evaluation methods of the samples (toners of Examples 1 to 9 and Comparative Examples 1 to 5) are as follows.

(Average circularity)
Using a flow-type particle image analyzer (“FPIA (registered trademark) -3000” manufactured by Sysmex Corporation), the circularity of the samples (the toners of Examples 1 to 9 and External Examples 1 to 5 before external addition) was measured. It was measured. Specifically, the circularity of each of the 3000 toner particles contained in the sample was measured, and the average value of the measured 3000 circularity was used as the evaluation value.

(Method for taking TEM photograph of cross section of toner particles)
First, a sample (toner) was dispersed in a room temperature curable epoxy resin and allowed to stand in an atmosphere of 40 ° C. for 2 days to obtain a cured product. The obtained cured product was dyed with osmium tetroxide. Thereafter, a thin sample for cross-sectional observation of toner particles having a thickness of 200 nm was cut out from the obtained cured product using a microtome (“EM UC6” manufactured by Leica Corporation). The obtained flake sample was observed with a transmission electron microscope (TEM, “JSM-6700F” manufactured by JEOL Ltd.) at a magnification of 3000 times and 10,000 times, and a TEM photograph of a cross section of the toner particles was taken.

(Charge decay coefficient)
The charge decay constant of the sample (toner) (the charge decay constant of the toner base particles) was measured using an electrostatic diffusivity measuring device (“NS-D100” manufactured by Nano Seeds Co., Ltd.). The method for measuring the charge decay constant of the toner will be described in detail below.

  A sample (toner) was placed in the measurement cell. The measurement cell was a metal cell in which a recess having an inner diameter of 10 mm and a depth of 1 mm was formed. The sample was pushed in from above using a slide glass, and the concave portion of the cell was filled with the sample. The sample overflowed from the cell was removed by reciprocating the slide glass on the surface of the cell. The sample filling amount was 0.05 g.

Subsequently, the measurement cell filled with the sample was left in an environment of a temperature of 23 ° C. and a humidity of 50% RH for 24 hours. Subsequently, the grounded measurement cell was placed in an electrostatic diffusivity measuring apparatus, and ions were supplied to the sample by corona discharge to charge the sample. And after 0.7 second passed after completion | finish of corona discharge, the surface potential of the sample was measured continuously. The measurement conditions were a discharge voltage of 6 kV, a discharge time of 0.5 seconds, a gap between the measurement part and the sample can of 1 mm, a frequency of 1 Hz, and a measurement time of 240 seconds. The charge decay constant α was calculated from the equation “V = V ₀ exp (α√t)” using the measured surface potential. In the formula, V represents the surface potential [V], V ₀ represents the initial surface potential [V], and t represents the decay time [second].

(Heat resistant storage stability)
The heat resistant storage stability of the sample (toner) was evaluated according to the following method.

A sample for evaluation of heat-resistant storage stability was obtained by weighing 2 g of a sample (toner) into a 20 mL capacity plastic container and leaving it in a thermostat set at 60 ° C. for 3 hours. Thereafter, the sample for heat resistant storage stability evaluation was sieved using a 200 mesh (mesh 75 μm) sieve under the conditions of rheostat scale 5 and time 30 seconds according to the manual of a powder tester (manufactured by Hosokawa Micron Corporation). . After sieving, the mass of the sample remaining on the sieve was measured. From the mass of the sample before sieving and the mass of the sample remaining on the sieving after sieving, the degree of aggregation (% by mass) of the sample was calculated according to the following formula. From the calculated degree of aggregation, the heat resistant storage stability of the sample was evaluated according to the following criteria.
Aggregation degree (mass%) = (mass of sample remaining on sieve / mass of sample before sieving) × 100
A (very good): The degree of aggregation of the sample is 20% by mass or less.
○ (Good): The degree of aggregation of the sample exceeds 20% by mass and is 40% by mass or less.
X (not good): The degree of aggregation of the sample exceeds 40% by mass.

  The low-temperature fixability, transfer efficiency, and cleaning property of each sample (toner) were evaluated using a two-component developer adjusted according to the following method.

  A developer carrier (Kyocera Document Solutions Co., Ltd., “TASKalfa 5550” carrier) and 11% by mass of toner with respect to the mass of the carrier are mixed for 30 minutes using a ball mill, and evaluated as a two-component developer. Was prepared.

(Transfer efficiency)
The developer obtained above was mounted in a yellow developing machine of a color multifunction peripheral (“TASKalfa 5550ci” manufactured by Kyocera Document Solutions Inc.). After adjusting the development conditions so that the toner adhesion amount on the drum after development is 5 mg / cm ² , continuous printing of 2,000 sheets under the conditions of a temperature of 20 ° C. and a humidity of 65% RH and a printing rate of 5% And printed. The transfer efficiency of the sample was calculated by measuring the amount of developed toner and the amount of toner collected at the cleaning section. The transfer efficiency of the sample was evaluated according to the following criteria.
A (very good): The transfer efficiency of the sample is 90% or more.
○ (Good): The transfer efficiency of the sample is 80% or more and less than 90%.
X (not good): The transfer efficiency of the sample is less than 80%.

(Cleanability)
Further, as described above, the presence or absence of occurrence of image noise corresponding to the toner drop from the cleaning unit after continuous printing of 2,000 sheets was visually determined. Further, the fog density (FD) of the sample was measured for the case where image noise corresponding to toner dropping occurred. Note that the fog density (FD) of the sample is a value obtained by subtracting the image density of the blank paper before image output from the image density of the blank portion of the patch pattern. For measurement of the fog density (FD) of the sample, a fully automatic whiteness meter (“TC-6MC” manufactured by Tokyo Denshoku Co., Ltd.) was used. The cleanability of the sample was evaluated according to the following criteria.
A (very good): No toner dropout.
○ (Good) The toner is removed but the fog density (FD) of the sample is 0.01 or less.
X (not good): There is toner dropping, and the fog density (FD) of the sample is 0.01 or more.

[Evaluation results]
The evaluation results for each of the toners are as follows. Table 1 shows the measurement results of the average circularity of the toner base particles, the shell layer thickness, the toner charge attenuation coefficient, the heat resistant storage stability of the toner, the toner transferability, and the toner cleaning property.

  It can be understood that the toners of Examples 1 to 9 are excellent in heat-resistant storage stability, transferability, and cleaning properties. It can be understood that the toners of Comparative Examples 1 to 5 are inferior to the toners of Examples 1 to 9 in at least one of heat-resistant storage property, transfer property, and cleaning property.

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

Claims (5)

An electrostatic latent image developing toner containing toner particles including toner mother particles,
The toner base particles include a toner core and a shell layer covering the toner core;
The shell layer includes a thermosetting component;
The toner mother particles have an average circularity of 0.965 or more and 0.980 or less,
Electrostatic latent image development in which the toner particles have a charge decay coefficient of 0.007 or more and 0.030 or less, measured after leaving the toner particles in an environment of temperature 23 ° C. and humidity 50% RH for 24 hours or more. Toner. The toner particles include an external additive,
The electrostatic latent image developing toner according to claim 1, wherein the external additive is externally added to the surface of the toner base particles.   The electrostatic latent image developing toner according to claim 1, wherein the external additive is one or more inorganic particles containing at least silica.   The electrostatic latent image developing toner according to claim 1, wherein the shell layer has a thickness of 15 nm or less.   The toner for developing an electrostatic latent image according to any one of claims 1 to 4, which is used in a tandem electrophotographic image forming apparatus as a color image forming apparatus.