JP7115161B2 - black toner - Google Patents

Description

The present invention relates to black toner.

For example, Patent Literature 1 discloses a technique for producing a toner by aggregating polyester resin particles in an aqueous medium.

JP 2015-125404 A

In the toner described in Patent Document 1, most of the toner particles are composed of a binder resin. With such a toner, there is a limit to simultaneously achieving heat-resistant storage stability, low-temperature fixability, color developability when used as a black toner, and suppression of adhesion to a photoreceptor drum.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a black toner which is excellent in heat-resistant storage stability, low-temperature fixability and color-developing properties, and which hardly adheres to a photoreceptor drum.

The black toner of the present invention contains toner particles. The toner particles adhere to a toner core containing a release agent having a carboxyl group, a shell layer partially covering the surface of the toner core, and portions of the surface of the toner core not covered with the shell layer. and magnetic particles. At least part of the surface of the magnetic particles is exposed from the shell layer, and protrudes radially outward of the toner core from the surface of the shell layer. The content of the magnetic particles is 0.1 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the toner core. The shell layer contains a shell resin having an unopened oxazoline group. The content of unopened oxazoline groups measured by gas chromatography-mass spectrometry is 490 μmol/g or more and 1,500 μmol/g or less. In measurement by differential scanning calorimetry, the endothermic amount derived from melting of the release agent is 80 mJ/mg or more and 160 mJ/mg or less.

The black toner of the present invention is excellent in heat-resistant storage stability, low-temperature fixability, and color development, and can suppress adhesion to a photoreceptor drum.

FIG. 3 is a diagram showing an example of the cross-sectional structure of toner particles contained in the black toner according to the embodiment of the invention; 5 is a graph showing an example of a differential scanning calorimetry spectrum of black toner according to an embodiment of the present invention; 5 is a graph showing an example of a G' temperature dependency curve of black toner according to an embodiment of the invention;

Preferred embodiments of the present invention are described below. Note that the toner is an aggregate (for example, powder) of toner particles. The external additive is an aggregate (for example, powder) of external additive particles. Evaluation results (values indicating shape, physical properties, etc.) regarding powder (more specifically, powder of toner particles, powder of external additive particles, etc.) are the It is the number average of the values measured for each of the selected particles.

The measured value of the volume median diameter (D ₅₀ ) of the powder was measured using a laser diffraction/scattering particle size distribution analyzer ("LA-950" manufactured by Horiba, Ltd.) unless otherwise specified. is the median diameter.

Unless otherwise specified, the number average primary particle diameter of the powder is the circle-equivalent diameter of the primary particles measured using a scanning electron microscope (Heywood diameter: a circle having the same area as the projected area of the primary particles diameter). The number average primary particle diameter of the powder is, for example, the number average value of equivalent circle diameters of 100 primary particles. The number average primary particle size of particles refers to the number average primary particle size of particles in powder unless otherwise specified.

Chargeability means chargeability in triboelectrification unless otherwise specified. The strength of positive chargeability (or the strength of negative chargeability) in triboelectrification can be confirmed by a known electrification series or the like. For example, toner is mixed with standard carriers provided by the Imaging Society of Japan (standard carrier for negatively charged toner: N-01, standard carrier for positively charged toner: P-01). electrify. Before and after triboelectrification, the charge amount of the object to be measured is measured with, for example, a charge amount measuring device (Q/m meter). indicates that

The glass transition point (Tg) is a value measured according to "JIS (Japanese Industrial Standards) K7121-2012" using a differential scanning calorimeter ("DSC-6220" manufactured by Seiko Instruments Inc.) unless otherwise specified. is. In the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured with a differential scanning calorimeter, the temperature at the inflection point caused by the glass transition (specifically, the extrapolated line of the baseline and the falling edge The temperature at the intersection of the line with the extrapolated line) corresponds to Tg (glass transition point).

A "major component" of a material means, by mass, the component that is the most abundant in the material, unless otherwise specified.

Hereinafter, compounds and their derivatives may be collectively referred to by adding "system" after the compound name. When the polymer name is expressed by adding "system" after the compound name, it means that the repeating unit of the polymer is derived from the compound or its derivative. Acryl and methacryl may be collectively referred to as "(meth)acryl". Unless otherwise specified, each component described below may be used singly or in combination of two or more.

<Black Toner>
The black toner (hereinafter sometimes referred to as “toner”) according to the exemplary embodiment contains toner particles. The toner particles comprise a toner core containing a release agent having a carboxyl group, a shell layer partially covering the surface of the toner core, and magnetic particles adhering to portions of the surface of the toner core that are not covered with the shell layer. Prepare. At least part of the surface of the magnetic particles is exposed from the shell layer, and protrudes radially outward of the toner core from the surface of the shell layer. The content of the magnetic particles is 0.1 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the toner core. The shell layer contains a shell resin having an unopened ring oxazoline group. The content of unopened oxazoline groups measured by gas chromatography-mass spectrometry is 490 μmol/g or more and 1,500 μmol/g or less. In measurement by differential scanning calorimetry, the endothermic amount derived from melting of the release agent is 80 mJ/mg or more and 160 mJ/mg or less.

The toner is suitable for developing electrostatic latent images, for example, as a positively charged toner. The toner may be used as a single component developer. The toner may be mixed with a carrier using a mixing device (eg, ball mill) and used as a two-component developer. When used as a one-component developer, the toner is positively charged by friction with a developing sleeve or a toner charging member in the developing device. Examples of the toner charging member include a doctor blade. In the case of forming a two-component developer, the toner is positively charged by friction with the carrier in the developing device.

The details of the toner will be described below with appropriate reference to the drawings.

[Toner particles]
FIG. 1 shows an example of a cross-sectional structure of toner particles 10 contained in toner. As shown in FIG. 1, the toner particles 1 consist of a toner core 11, a shell layer 12 that partially covers the surface of the toner core 11, and a magnetic layer that adheres to portions of the surface of the toner core 11 that are not covered with the shell layer 12. and particles 13 . Part of the surface of magnetic grain 13 is exposed from shell layer 12 . Further, the magnetic particles 13 protrude radially outward of the toner core 11 from the surface of the shell layer 12 .

However, the toner particles 1 shown in FIG. 1 are merely an example of toner particles contained in the toner. Specifically, the magnetic particles need only cover at least a portion of the surface of the toner core that is not covered with the shell layer. As shown in FIG. It is not necessary to cover all the uncovered portions. For example, a portion of the surface of the toner core may be exposed without being covered by either the shell layer or the magnetic particles. Further, since the magnetic particles can improve the adhesiveness with the toner core 11, it is preferable that the magnetic particles adhere to the toner core 11 in a state of being bitten into, as shown in FIG. Further, additive particles may be dispersed in the shell layer. Furthermore, the toner particles may further comprise an external additive adhering to the surface of the shell layer. In addition, in toner particles further comprising an external additive, particles constituted by a toner core, a shell layer, and magnetic particles correspond to toner base particles.

FIG. 2 is a graph showing an example of DSC data measured using a differential scanning calorimeter when the temperature is raised for the second time. The rate of temperature increase and the rate of temperature decrease during measurement can each be, for example, 10° C./min. The graph in FIG. 2 shows an endothermic curve with heat flow (DSC signal) on the vertical axis and temperature on the horizontal axis.

In FIG. 2, the endothermic amount ΔH [mJ/mg] derived from melting of the release agent per 1 mg of toner can be obtained from the area S of the endothermic peak derived from melting of the release agent contained in the toner.

ΔH is 80 mJ/mg or more and 160 mJ/mg or less, preferably 100 mJ/mg or more and 140 mJ/mg or less. By setting ΔH to 80 mJ/mg or more, low-temperature fixability can be improved. By setting ΔH to 160 mJ/mg or less, the heat-resistant storage stability can be improved.

The black toner according to the exemplary embodiment has the above-described structure, so that it is excellent in heat-resistant storage stability, low-temperature fixability, and color development, and can suppress adhesion to the photoreceptor drum. The reason is explained below. A larger value of ΔH of the toner tends to indicate a larger content of the release agent. A toner having a ΔH within the above numerical range is a general toner (for example, approximately 90% by mass of a binder resin, approximately 5% by mass of a release agent, and approximately 5% by mass of a colorant). It contains a large amount (for example, 10 to 20 times) of the release agent compared to the toner it contains. Here, when a large amount of a release agent is added to a general toner, the low-temperature fixability is improved, but the toner particles tend to aggregate due to the detachment of the release agent at high temperatures, and the surface becomes rough. It becomes easy to adhere to other members of the image forming apparatus (for example, a photosensitive drum, etc.). Therefore, a toner containing a large amount of release agent is inferior in heat-resistant storage stability, and tends to adhere to a photosensitive drum or the like to cause image defects.

On the other hand, in the present embodiment, since the surface of the toner core is coated with the shell layer, the toner can exhibit excellent low-temperature fixability while suppressing the above-described decrease in heat-resistant storage stability and adhesion to the photoreceptor drum. . In the toner, the release agent has a carboxy group, the shell resin contained in the shell layer has an unopened ring oxazoline group, and the content of the unopened ring oxazoline group is within a certain range. Therefore, in the toner, a covalent bond (amide ester bond) is formed between the release agent and the shell resin in an appropriate ratio, and the toner core and the shell layer adhere to each other appropriately. , deterioration of heat-resistant storage stability and adhesion to the photoreceptor drum can be more effectively suppressed. Furthermore, the toner has magnetic particles with relatively high hardness attached to the surface of the toner core. Since the magnetic particles adhere to the relatively soft toner core rather than the relatively hard shell layer, they are less likely to detach from the toner particles. In addition, since at least part of the surface of the magnetic particles is exposed from the shell layer and protrudes radially outward of the toner core from the surface of the shell layer, the photosensitive drum can be polished (cleaned). Therefore, the magnetic particles more effectively suppress adhesion of toner to the photosensitive drum. Furthermore, most of the inorganic particles (e.g., titanium oxide particles) that are generally added to the toner have a color other than black (e.g., white), whereas the magnetic particles are relatively close to black, so the toner color developability is improved. is difficult to reduce. Further, the magnetic particles can moderately roughen the surface of the formed image and moderately suppress glossiness. Therefore, the toner has excellent color developing properties.

In addition, the magnetic particles adhering to the toner core have the function of suppressing the leakage of toner core components and the function of spacers that suppress the contact between toner particles, thereby improving the heat-resistant storage stability of the toner. contribute.

The toner preferably has a sharp melt property in order to achieve both heat-resistant storage stability and low-temperature fixability. Specifically, in the toner, the temperature at which the storage elastic modulus becomes 1.0×10 ⁸ Pa (hereinafter sometimes referred to as “first temperature”) is preferably 70° C. or higher. Further, in the toner, the temperature at which the storage elastic modulus becomes 1.0×10 ⁵ Pa (hereinafter sometimes referred to as “second temperature”) is preferably 85° C. or lower. A toner having such properties has a high storage elastic modulus at 70° C. or lower, and exhibits excellent storage stability. It lowers and exhibits excellent fixability. Toners having such sharp-melt properties tend to be excellent in both heat-resistant storage stability and low-temperature fixability. The storage elastic modulus of the toner is a value measured by a rheometer.

FIG. 3 shows an example of the G' temperature dependence curve (vertical axis: storage elastic modulus, horizontal axis: temperature) of the toner having sharp meltability. Specifically, FIG. 3 shows an example of the results of measuring the storage elastic modulus at each temperature while increasing the temperature of the toner at a constant rate (heating rate of 4° C./min) using a rheometer. In the G' temperature dependence curve shown in FIG. 3, the storage elastic modulus decreases as the temperature of the toner rises. In the toner shown in FIG. 3, the first temperature at which the storage elastic modulus is 1.0×10 ⁸ Pa is 70° C. or higher, and the second temperature at which the storage elastic modulus is 1.0×10 ⁵ Pa is 85° C. or lower. .

The first temperature is more preferably 70° C. or higher and 80° C. or lower, and even more preferably 70° C. or higher and 75° C. or lower. In addition, the second temperature is more preferably 80° C. or higher and 90° C. or lower, and still more preferably 80° C. or higher and 85° C. or lower. Further, the glass transition point of the toner is preferably 65° C. or higher and 70° C. or lower from the viewpoint of further improving the above-mentioned sharp melt property.

From the viewpoint of obtaining a toner having even better low-temperature fixability and heat-resistant storage stability, the thickness of the shell layer is preferably 10 nm or more and 100 nm or less. The thickness of the shell layer can be measured by analyzing a cross-sectional TEM (transmission electron microscope) image of the dyed toner particles using commercially available image analysis software (eg, "WinROOF" manufactured by Mitani Shoji Co., Ltd.). . If the thickness of the shell layer is not uniform in one toner particle, four evenly spaced points (specifically, two straight lines perpendicular to each other at approximately the center of the cross section of the toner particle are drawn and the two straight lines are drawn. The thickness of the shell layer is measured at each of the four points where the straight line intersects the shell layer, and the arithmetic average of the obtained four measured values is taken as the evaluation value (thickness of the shell layer) of the toner particles.

On the surface of the toner core, the area ratio of the region covered with the shell layer (shell layer coverage) is preferably 90% or more, more preferably 95% or more. By setting the coverage of the shell layer to 90% or more, it is possible to obtain a toner having even better heat-resistant storage stability. The coverage of the shell layer can be measured by analyzing a cross-sectional TEM (transmission electron microscope) image of the toner particles using commercially available image analysis software (eg, "WinROOF" manufactured by Mitani Shoji Co., Ltd.). Specifically, in a TEM image of a cross section of a dyed toner particle, the coverage ratio of the shell layer is obtained by measuring the ratio of the area covered with the shell layer to the surface area of the toner core (outline indicating the outer edge). be done.

[Toner Core]
The toner core contains a release agent having a carboxy group. The toner core may further contain an internal additive (for example, at least one of a colorant, a charge control agent, and magnetic particles) in addition to the release agent, if necessary.

In order to obtain a toner suitable for image formation, the volume median diameter (D ₅₀ ) of the toner core is preferably 4 μm or more and 9 μm or less.

(Release agent)
A release agent has a carboxy group. Wax is preferred as the release agent. Examples of wax include ester wax, polyethylene wax, polypropylene wax, fluororesin wax, Fischer-Tropsch wax, paraffin wax, and montan wax. When the release agent is a mixture of a plurality of compounds, at least one compound of the release agent should have a carboxy group.

Ester wax (more specifically, synthetic ester wax or natural ester wax) is preferable as the wax. By using a synthetic ester wax as the release agent, it becomes easier to adjust the melting point of the release agent to a desired range. A synthetic ester wax can be synthesized, for example, by reacting an alcohol with a carboxylic acid (or a carboxylic acid halide) in the presence of an acid catalyst. Raw materials for synthetic ester waxes may be substances derived from natural products (eg, long-chain fatty acids prepared from natural oils and fats), or commercially available synthetic products. Carnauba wax or rice wax is preferred as the natural ester wax. From the viewpoint of securing a sufficient amount of carboxy groups, the acid value of the release agent is preferably 1.0 mgKOH/g or more, more preferably 1.0 mgKOH/g or more and 10.0 mgKOH/g or less, and 1.0 mgKOH/g or more. more preferably 3.0 mgKOH/g or less.

The content of the release agent in the toner core is preferably 60% by mass or more and 95% by mass or less, more preferably 85% by mass or more and 95% by mass or less.

(coloring agent)
The toner core preferably contains a colorant. As the coloring agent, known pigments or dyes can be used, and examples thereof include black coloring agents and color coloring agents. When the toner core contains a colorant, the content thereof is 1.0 parts by mass or more and 20.0 parts by mass with respect to 100 parts by mass of the release agent from the viewpoint of improving the image quality of the image formed by the toner. The following is preferable, and 3.0 parts by mass or more and 15.0 parts by mass or less is more preferable.

Examples of black colorants include carbon black. Color colorants include, for example, yellow colorants, magenta colorants, and cyan colorants. Coloring agents can be used in combination to produce a black tone.

Yellow colorants include, for example, condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds. 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, and 194), Naphthol Yellow S, Hansa Yellow G, and C.I. I. Bat yellow is mentioned.

Magenta colorants include, for example, condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. Examples of magenta coloring agents 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, and 254).

Cyan colorants include, for example, copper phthalocyanine compounds, anthraquinone compounds, and basic dye lake compounds. Cyan colorants include, for example, C.I. I. pigment blue (1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, and 66), phthalocyanine blue, C.I. I. bat blue, and C.I. I. acid blue.

(Charge control agent)
The toner core may contain charge control agents. A charge control agent is used, for example, for the purpose of improving the charging stability or charging rise characteristics of the toner. Here, the charging rise characteristic of the toner is an index of whether or not the toner can be charged to a predetermined charging level in a short time.

By incorporating a negative charge control agent (more specifically, an organic metal complex, a chelate compound, or the like) into the toner core, the anionicity of the toner core can be enhanced. In addition, the cationic property of the toner core can be enhanced by incorporating a positive charge control agent (more specifically, pyridine, nigrosine, quaternary ammonium salt, etc.) into the toner core. However, if the toner has sufficient chargeability, the toner core does not need to contain a charge control agent.

(Binder resin)
Since the toner core contains a relatively large amount of release agent, the toner can be imparted with characteristics suitable for image formation without containing a binder resin. However, the toner core may contain a small amount of binder resin for the purpose of improving adhesion to the shell layer and improving heat resistant storage stability. The content of the binder resin in the toner core is preferably 15% by mass or less, more preferably 5% by mass or less, and even more preferably 0% by mass.

As the binder resin, a polymer of a monomer (resin raw material) containing a styrene-based monomer, a (meth)acrylic acid alkyl ester, and (meth)acrylic acid is preferable. By using such a polymer as a binder resin, it is possible to introduce a sufficient amount of carboxy groups into the toner core while improving the fixability of the toner. Styrenic monomers include, for example, styrene, alkylstyrene (more specifically, α-methylstyrene, p-ethylstyrene, 4-tert-butylstyrene, etc.), hydroxystyrene (more specifically, p- hydroxystyrene, m-hydroxystyrene, etc.), and halogenated styrenes (more specifically, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc.). Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, iso-propyl (meth)acrylate, and n-(meth)acrylate. -butyl, iso-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[Magnetic particles]
The magnetic particles adhere to those portions of the toner core surface that are not covered by the shell layer. The magnetic particles polish (clean) the surface of the photoreceptor drum and suppress adhesion of toner to the photoreceptor drum. In addition, since the magnetic particles have a black appearance and moderately roughen the surface of the formed image (provide a matte texture), they improve the color developability of the toner.

Materials for the magnetic particles include, for example, ferromagnetic metals (such as iron, cobalt and nickel) or their alloys, ferromagnetic metal oxides (such as ferrite, magnetite, and chromium dioxide), and ferromagnetic treatment. (for example, a carbon material to which ferromagnetism is imparted by heat treatment). The toner may contain magnetic particles adhering to the surface of the toner core, and further contain magnetic particles in other parts (for example, inside the toner core or on the surface of the shell layer). In the toner, when there are magnetic particles adhering to the surface of the toner core and magnetic particles contained in other parts, the ratio of the magnetic particles adhering to the surface of the toner core to the total magnetic particles is 60% by mass or more. Preferably, 90% by mass or more is more preferable.

The magnetic particles are preferably surface-treated. Metal ions (for example, iron ions) are less likely to elute from the surface-treated magnetic particles. Here, when the shell layer is formed on the surface of the toner core under acidic conditions, if metal ions are eluted on the surface of the toner core, the toner cores are likely to adhere to each other. On the other hand, when surface-treated magnetic particles are used, the elution of metal ions is suppressed, so it is thought that the sticking of toner cores to each other is suppressed.

The content of the magnetic particles is 0.1 parts by mass or more and 1.5 parts by mass or less, preferably 0.3 parts by mass or more and 0.8 parts by mass or less, relative to 100 parts by mass of the toner core. By setting the content of the magnetic particles to 0.1 parts by mass or more, the toner can be further improved in color developability, and adhesion of the toner to the photoreceptor drum can be more effectively suppressed. By setting the content of the magnetic particles to 1.5 parts by mass or less, the low-temperature fixability and color developability of the toner can be further improved.

[Shell layer]
The shell layer mainly contains a shell resin having an oxazoline group. As the shell layer, a layer substantially composed of a shell resin (for example, a layer having a shell resin content of 90% by mass or more) is preferable, and a layer containing only the shell resin is more preferable. At least part of the oxazoline groups of the shell resin are preferably crosslinked with the release agent in the toner core.

As the shell resin, a repeating unit represented by the following general formula (1) (hereinafter sometimes referred to as "first repeating unit") and a repeating unit represented by the following general formula (2) (hereinafter referred to as (sometimes referred to as a "second repeating unit").

In general formula (I), R ¹ represents a hydrogen atom or an alkyl group having from 1 to 10 carbon atoms which may be substituted with a phenyl group. In general formula (II), R ² represents a hydrogen atom or an alkyl group having from 1 to 10 carbon atoms which may be substituted with a phenyl group. * represents a bonding site with an atom contained in the release agent (the release agent contained in the toner core).

R ¹ and R ² are preferably a hydrogen atom, a methyl group, an ethyl group, or an isopropyl group.

An oxazoline group (unopened ring) has a strong positive charge. Therefore, by using a resin having an oxazoline group as the shell resin, it is possible to provide a positively chargeable toner with excellent charging characteristics.

The shell resin may further have a repeating unit represented by general formula (III) below.

In general formula (III), R ³ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms which may be substituted with a phenyl group. R ⁴ represents an alkyl group having 1 to 3 carbon atoms.

R ³ is preferably a hydrogen atom, a methyl group, an ethyl group, or an isopropyl group. R ⁴ is preferably a methyl group.

The mass average molecular weight of the shell resin is preferably 5,000 or more and 50,000 or less, more preferably 5,000 or more and 30,000 or less.

The shell resin may further have repeating units derived from other vinyl compounds in addition to repeating units (I) to (III). Other vinyl compounds include, for example, ethylene, propylene, butadiene, vinyl chloride, (meth)acrylic acid, (meth)acrylic acid esters, acrylonitrile, and styrene. The (meth)acrylic acid ester is preferably an alkyl (meth)acrylate, more preferably methyl (meth)acrylate or ethyl (meth)acrylate, and still more preferably methyl methacrylate.

[External Additive]
The toner particles may further comprise an external additive adhered to the surface of the shell layer. The external additive includes external additive particles. Inorganic particles are preferable as the external additive particles. Inorganic particles include, for example, silica particles and particles of metal oxides (more specifically, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate). Silica particles or titanium oxide particles are preferable as the inorganic particles. The number average primary particle diameter of the inorganic particles is preferably 1 nm or more and 100 nm or less, more preferably 5 nm or more and 40 nm or less.

When the toner particles contain inorganic particles, the content thereof is preferably 0.01 parts by mass or more and 10.0 parts by mass or less, and 0.1 parts by mass or more and 5.0 parts by mass with respect to 100 parts by mass of the toner base particles. Part or less is more preferable.

[Toner manufacturing method]
A method for manufacturing the toner will be described below. A toner manufacturing method comprises a step of preparing a toner core (toner core preparing step), a step of attaching magnetic particles to the surface of the toner core (magnetic particle attaching step), and at least a region of the surface of the toner core not covered with the magnetic particles. and a step of covering a portion with a shell layer (shell layer forming step). In the shell layer forming step, the thickness of the shell layer is adjusted so that at least part of the surface of the magnetic particles is exposed from the shell layer and the magnetic particles protrude radially outward of the toner core from the surface of the shell layer. . As a result, toner base particles comprising a toner core, magnetic particles, and a shell layer are obtained. The obtained toner base particles may be used as toner particles as they are, or may be used as toner particles after adhering an external additive to the surface thereof. That is, the toner manufacturing method may further include a step of attaching an external additive to the surface of the toner base particles (external addition step). Each step will be described in detail below.

[Toner core preparation process]
In this step, a toner core is prepared. The method for preparing the toner core is not particularly limited, and a known pulverization method or a known agglomeration method can be used, but the agglomeration method is preferably used.

In one example of the pulverization method, first, a release agent and an internal additive added as necessary are mixed. Subsequently, the obtained mixture is melt-kneaded using a melt-kneading device (for example, a single-screw or twin-screw extruder). Subsequently, the obtained melt-kneaded product is pulverized and classified. A toner core is thus obtained.

In one example of the aggregation method, first, in an aqueous medium containing fine particles of each of the release agent and the internal additive added as necessary, these fine particles are aggregated to a desired particle size. As a result, aggregated particles containing a releasing agent and the like are formed. Subsequently, the obtained aggregated particles are heated to coalesce the components contained in the aggregated particles. A toner core is thus obtained.

[Magnetic particle adhesion step]
In this step, magnetic particles are attached to the surface of the toner core. A specific method of adhering the magnetic particles includes, for example, a method of mixing the toner cores and the magnetic particles using a mixer (for example, “Multi-Purpose Mixer” manufactured by Nippon Coke Kogyo Co., Ltd.).

[Shell layer forming step]
In this step, at least a portion of the area of the surface of the toner core that is not covered with the magnetic particles is covered with the shell layer. Methods of coating with a shell layer include, for example, an in-situ polymerization method, an in-liquid curing coating method, and a coacervation method. More specifically, a raw material for forming a shell layer (shell raw material) and toner cores to which magnetic particles are attached are put into an aqueous medium, and then the aqueous medium is heated to obtain the shell raw material. A method of allowing a reaction (for example, a thermosetting reaction) to proceed in a region on the surface of the toner core where the magnetic particles are not adhered to form a shell layer in this region can be used. In this method, the thickness of the shell layer can be adjusted by changing the amount of shell raw material used (converted to solid content).

In this step, a carboxylic acid having 2 to 4 carbon atoms (for example, acetic acid) may be added to the reaction solution. The amount of acetic acid added can be, for example, 0.1 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the toner core.

The shell raw material contains a vinyl resin for forming the shell layer (vinyl resin for shell layer formation). The shell layer-forming vinyl resin contains an oxazoline group. The shell layer-forming vinyl resin has, for example, the first repeating unit described above. When the shell layer-forming vinyl resin has the first repeating unit, in this step, at least part of the oxazoline group of the first repeating unit and at least part of the carboxyl group of the release agent contained in the toner core are crosslinked. A structure is formed, and the second repeating unit is formed in the shell layer-forming vinyl resin. Further, in this step, when a carboxylic acid is added to the reaction solution, the third repeating unit is formed in the shell layer-forming vinyl resin by the reaction of at least part of the first repeating unit with the added carboxylic acid. be. Thus, the shell resin is formed by the reaction between the shell layer-forming vinyl resin and the releasing agent or the carboxylic acid.

As the shell raw material, for example, "Epocross (registered trademark) WS-300" or "Epocross (registered trademark) WS-700" manufactured by Nippon Shokubai Co., Ltd. can be used. “Epocross® WS-300” contains a copolymer (water-soluble cross-linking agent) of 2-vinyl-2-oxazoline and methyl methacrylate. The mass ratio of the monomers constituting the copolymer was (2-vinyl-2-oxazoline):(methyl methacrylate)=9:1. “Epocross® WS-700” contains a copolymer (water-soluble cross-linking agent) of 2-vinyl-2-oxazoline, methyl methacrylate and butyl acrylate. The mass ratio of the monomers constituting the copolymer was (2-vinyl-2-oxazoline):(methyl methacrylate):(butyl acrylate)=5:4:1.

[External addition process]
In this step, an external additive is adhered to the surface of the toner base particles. A specific method of adhering the external additive includes, for example, a method of mixing the toner base particles and the external additive using a mixer (for example, “Multipurpose Mixer” manufactured by Nippon Coke Kogyo Co., Ltd.). As a result, a toner containing toner particles having the toner base particles and the external additive adhering to the surfaces of the toner base particles is obtained.

EXAMPLES Hereinafter, the present invention will be described more specifically using examples. However, the present invention is in no way limited to the scope of the examples.

(Magnetic powder)
The magnetic powder (powder containing magnetic particles) used in the examples and the titanium oxide powder used instead of the magnetic powder in the comparative examples will be described.
Magnetic powder (Y-1): sample product manufactured by Toda Kogyo Co., Ltd., particle shape: octahedron, average particle size: 200 nm, saturation magnetization: 85.5 Am ² /kg, main component: ferrite Magnetic powder (Y-2): Sample product manufactured by Toda Kogyo Co., Ltd., particle shape: spherical, average particle size 190 nm, saturation magnetization 80.0 Am ² / kg, main component: ferrite Titanium oxide powder (y-1): Titan Kogyo Co., Ltd. "EC- 100", average particle size 300 nm, main component: titanium oxide

[Toner manufacturing]
(Preparation of release agent dispersion (x-1))
530.0 g of demineralized water, 450.0 g of high-purity solid ester wax ("Nissan Electol (registered trademark) WEP-9" manufactured by NOF Corporation, acid value: 1.5 mg KOH / g) as a release agent, 20.0 g of an anionic surfactant (“Neogen (registered trademark) SC” manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., component: sodium dodecylbenzenesulfonate, active ingredient: 66% by mass) was mixed. Subsequently, the resulting mixture was emulsified by high-pressure shearing using a Gorlin homogenizer (“APV (registered trademark)” manufactured by SPX). As a result, 1,000.0 g of release agent dispersion (x-1) was obtained.

Release agent dispersions (x-2) to (x-5) were prepared in the same manner as the release agent dispersion (x-1) except for the following changes. In the preparation of the release agent dispersion (x-1), the amounts of demineralized water, release agent, and anionic surfactant added were as described above. In preparation 5), the amounts of demineralized water, release agent and anionic surfactant added were as shown in Table 1 below.

(Preparation of toner core)
1,000.0 g of the release agent dispersion (x-1) and 100.0 g of the colorant dispersion were charged into a 2 L reaction vessel equipped with an anchor-type stirring blade with a baffle plate. The colorant dispersion was an aqueous dispersion of a colorant (carbon black) ("REGAL (registered trademark) 330R" manufactured by Cabot Corporation, component: solid content concentration: 35% by mass) (input amount of colorant: 35% by mass). 0g).

Subsequently, while stirring the contents of the container, a flocculant (aqueous solution of aluminum sulfate) was added dropwise into the container. In the dropping of the coagulant, the total dropping amount was 4 g (solid content conversion value of aluminum sulfate), and the dropping rate was 0.2 g (solid content conversion value of aluminum sulfate)/min. After the dropping of the flocculant was completed, the temperature of the contents of the container was raised to 50°C at a rate of 1°C/min while stirring the contents of the container. The temperature of the contents of the container was 30° C. at the start of the temperature rise. After completion of the temperature rise, the contents of the container were held at 50° C. for 1 hour to promote aggregation of the particles in the container and granulate. As a result, aggregated particles having a volume median diameter (D ₅₀ ) of 7 μm were obtained.

When the volume median diameter of the aggregated particles in the container reached 7 μm, an aqueous solution of sodium dodecylbenzenesulfonate (an aqueous solution of “Neogen (registered trademark) SC” manufactured by Daiichi Kogyo Seiyaku Co., Ltd., solid content concentration 10) was added to the container. % by mass) was added in an amount of 2 g in terms of solid content. Thereafter, the temperature of the contents of the container was raised from 50° C. to 90° C. at a constant rate over 40 minutes, and then held at 90° C. for 2 hours. After that, the container contents were cooled at a constant rate to 40° C. over 10 minutes. Subsequently, the contents of the container were subjected to suction filtration using a Buchner funnel set with filter paper having an opening of 5 μm. Subsequently, the solid matter (powder) obtained by filtering the contents of the container (that is, solid-liquid separation) was washed with 5 L of ion-exchanged water. Four times the mass of ion-exchanged water was added to the washed solids to redisperse them, thereby obtaining a toner core dispersion having a solid content concentration of 20% by mass. A large number of toner cores were dispersed in the resulting toner core dispersion. Thereafter, the obtained toner core dispersion was dried, and the obtained powder was used as toner core (X-1). Toner core (X-1) had a composition corresponding to the amount of input material. Specifically, the toner core (X-1) had a “releasing agent/coloring agent” mass ratio of 90/7 (the content of the releasing agent in the solid content was 92.8% by mass). This corresponded to the ratio (90/7) of the mass of release agent (450.0 g) to the mass of colorant (35.0 g) used in the preparation of toner core (X-1).

Toner cores (X-2) to (X-6) were prepared in the same manner as toner core (X-1) except for the following changes. Release agent dispersion (x-1) was used in the preparation of toner core (X-1). On the other hand, in the preparation of toner cores (X-2) to (X-5), release agent dispersions (x-2) to (x-5) were used, respectively, as shown in Table 1 below. In the preparation of toner core (X-1), 100 g of colorant dispersion was added to 1,000.0 g of release agent dispersion (x-1). On the other hand, in the preparation of the toner core (X-6), 100.0 g of the colorant dispersion and 2.4 g of the magnetic powder (Y-1) were added to 1,000.0 g of the release agent dispersion (X-1). added.

(Magnetic powder adhesion process)
1.0 g (0.5 parts by mass) of magnetic powder (Y-1) containing a large number of magnetic particles was added to 200.0 g (100 parts by mass) of toner core (X-1), and an FM mixer (Nippon Coke Co., Ltd. (manufacturer) to attach the magnetic particles to the surface of the toner core (X-1). As a result, 201.0 g of powder having magnetic particles adhered to the surface of toner core (X-1) was obtained.

(Shell layer forming step)
A 1-liter three-necked flask equipped with a thermometer and stirring blades was set in a water bath, and the total amount (201.0 g) of the powder obtained in the step of adhering the magnetic powder and 600.0 g of purified water were placed in the flask. put in. After that, the temperature inside the flask was maintained at 40° C. using a water bath. Subsequently, 9.5 g of shell material was added into the flask and the contents of the flask were stirred at a rotation speed of 200 rpm for 1 hour. As the shell material, an oxazoline group-containing polymer aqueous solution (“Epocross (registered trademark) WS-300” manufactured by Nippon Shokubai Co., Ltd., monomer composition: methyl methacrylate/2-vinyl-2-oxazoline, solid content concentration: 10% by mass ) was used.

Subsequently, 8 mL of an aqueous ammonia solution with a concentration of 1% by mass was added into the flask. Subsequently, the temperature inside the flask was raised to 60° C. at a rate of 0.5° C./min while stirring the contents of the flask at a rotational speed of 150 rpm.

Subsequently, the temperature inside the flask was kept at 60° C. for 10 minutes while stirring the contents of the flask at a rotation speed of 100 rpm. Subsequently, the pH of the flask contents was adjusted to 7. An aqueous ammonia solution with a concentration of 1% by mass was used to adjust the pH. Subsequently, the contents of the flask were cooled to room temperature (about 25° C.) to obtain a dispersion liquid containing a large number of toner base particles.

(Washing process)
The dispersion liquid of the toner base particles obtained as described above was filtered (solid-liquid separation) using a Buchner funnel set with filter paper having an opening of 5 μm to obtain toner base particles in the form of a wet cake. After that, the resulting wet cake-like toner base particles were redispersed in ion-exchanged water. Further, filtration and dispersion were repeated to wash the toner base particles. For the washing of the toner base particles, dispersion and filtration were repeated five times in total until the conductivity of the filtrate (washing water) after washing became 1 μS/cm or less. An electrical conductivity meter "HORIBA (registered trademark) ES-51" manufactured by HORIBA, Ltd. was used for the measurement of electrical conductivity.

(Drying process)
Subsequently, the obtained toner base particles were treated with a continuous surface modification device (“Coat Mizer (registered trademark)” manufactured by Freund Corporation) under the conditions of a hot air temperature of 45°C and a blower air volume of 2 m ³ /min. dried. As a result, powder of dried toner base particles was obtained.

(External addition process)
Subsequently, using an FM mixer (manufactured by Nippon Coke Kogyo Co., Ltd.), 200 g of toner base particles and positively charged silica particles (“AEROSIL (registered trademark) REA90” manufactured by Nippon Aerosil Co., Ltd., content: positively charged by surface treatment) 3 g of dry silica particles imparted with properties, number average primary particle size: about 20 nm), and conductive titanium oxide particles (“EC-100” manufactured by Titan Kogyo Co., Ltd., substrate: TiO ₂ particles, coating layer: Sb-doped 3 g of SnO ₂ film) was added and mixed for 5 minutes. As a result, the external additives (silica particles and titanium oxide particles) adhered to the surface of the toner base particles. After that, sieving was performed using a 200-mesh (75 μm mesh) sieve. As a result, a toner (A-1) having a volume median diameter (D ₅₀ ) of 7 μm was obtained.

Toners (A-2) to (A-9) and (B-1) to (B-9) were produced in the same manner as toner (A-1) except for the following changes. .

Toner (A-1) was produced by using toner core (X-1), adding 9.5 g of shell material, and adding 1.0 g of magnetic powder (Y-1). On the other hand, in the production of toners (A-2) to (A-9), (B-1) to (B-6) and (B-8) to (B-9), the type of toner core and shell material The amount of addition, and the type and amount of magnetic powder added were as shown in Table 2 below. Incidentally, in the production of toner (B-9), 1.0 g of titanium oxide powder (y-1) was added instead of adding magnetic powder.

In the production of toner (A-1), acetic acid was not added in the formation of the shell layer. On the other hand, in the production of toner (A-4), immediately after the temperature inside the flask reached 60° C., 2.0 g of acetic acid having a concentration of 99% by weight was added into the flask at a constant rate in the formation of the shell layer.

Further, in the production of toner (A-1), the toner core (X-1) was used and the magnetic powder adhering step was carried out. On the other hand, in the production of toner (B-7), the toner core (X-6) was used and the magnetic powder adhesion step was not carried out. That is, in the production of toner (A-1), the powder obtained in the magnetic powder adhering step was used in the shell layer forming step. On the other hand, in the production of toner (B-7), 200.0 g of toner core (X-6) was used in place of the powder obtained in the magnetic powder adhering step in the shell layer forming step.

The obtained toners (A-1) to (A-9) and (B-1) to (B-9) were each treated with a room temperature curable epoxy resin ("Epon 815" manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.). and allowed to stand in an atmosphere of 40° C. for 2 days to obtain a cured product. The resulting cured product was dyed with osmium tetroxide. Then, using a microtome (“EM UC6” manufactured by Leica Corporation), a thin section sample with a thickness of 200 nm was cut out from the dyed cured product. The obtained flake sample was observed using a transmission electron microscope (TEM, "JSM-6700F" manufactured by JEOL Ltd.) at magnifications of 3,000 and 10,000, and TEM photographs of the cross section of the toner were taken. did. TEM photographs of the cross section of the toner show that the surface of the toner core is covered with the shell layer in toners (A-1) to (A-9), (B-1) to (B-6) and (B-9). It was confirmed that the magnetic particles (or titanium particles) adhered to the areas where the particles were not exposed. At least part of the surface of the magnetic particles in the toners (A-1) to (A-9), (B-1) to (B-6) and (B-9) is exposed from the shell layer, Moreover, it was confirmed that it protruded radially outward of the toner core from the surface of the shell layer. On the other hand, it was confirmed that the toner (B-7) contained magnetic particles in the toner core.

Regarding the toners (A-1) to (A-9) and (B-1) to (B-9), the content ratio of the unopened ring oxazoline group and the absorption resulting from melting of the release agent by differential scanning calorimetry. A calorific value measurement and a storage modulus measurement with a rheometer were performed. The measurement results are shown in Table 2 below.

[Measurement of Content Ratio of Unopened Ring Oxazoline Group]
The unopened ring oxazoline group content was measured by gas chromatography mass spectrometry (GC/MS method). In the GC / MS method, a gas chromatograph mass spectrometer (manufactured by Shimadzu Corporation "GCMS-QP2010 Ultra") and a multi-shot pyrolyzer (manufactured by Frontier Lab Co., Ltd. "FRONTIER LAB Multi-functional Pyrolyzer (registered Trademark) PY-3030D”) was used. The column used was a GC column (“Agilent (registered trademark) J&W Ultra Inert Capillary GC Column DB-5ms” manufactured by Agilent Technologies), phase: arylene phase obtained by introducing arylene into a siloxane polymer to strengthen the main chain of the polymer, inner diameter : 0.25 mm, film thickness: 0.25 μm, length: 30 m).

(Gas chromatograph)
・Carrier gas: helium (He) gas ・Carrier flow rate: 1 mL/min ・Vaporization chamber temperature: 210°C
・ Thermal decomposition temperature: Furnace "600°C", interface part "320°C"
Temperature rising conditions: After holding at 40° C. for 3 minutes, the temperature was raised from 40° C. to 300° C. at a rate of 10° C./min, and held at 300° C. for 15 minutes.

(mass spectrometry)
・Ionization method: EI (Electron Impact) method ・Ion source temperature: 200°C
・Interface temperature: 320℃
・Detection mode: Scan (measurement range: 45m/z to 500m/z)

By analyzing the mass spectrum measured under the above conditions, the peak derived from the unopened ring oxazoline group was identified, and based on the peak area of the measured chromatogram, the peak area of the unopened ring oxazoline group contained in the measurement target (toner) was determined. The amount (amount of unopened ring-opening oxazoline group contained in 1 g of toner) was determined. A calibration curve based on standard substances was used for quantification.

[Measurement of Endothermic Amount Derived from Melting of Release Agent by Differential Scanning Calorimetry]
A differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.) was used as a measuring device. By measuring the heat absorption curve of the toner using this measuring device, the amount of heat absorption (ΔH) resulting from the melting of the release agent was obtained. Specifically, 10 mg of toner was placed in an aluminum dish (container made of aluminum), and the aluminum dish was set in the measuring section of the measuring device. Also, an empty aluminum pan was used as a reference. In the measurement of the endothermic curve, the temperature of the measurement part was raised from the measurement start temperature of -20°C to 150°C at a rate of 10°C/min (RUN 1). After that, the temperature of the measurement part was lowered from 150°C to -20°C at a rate of 10°C/min. Subsequently, the temperature of the measurement part was again raised from -20°C to 150°C at a rate of 10°C/min (RUN2). By RUN2, an endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) of the sample was obtained. From the area of the endothermic peak in the obtained endothermic curve, the endothermic amount ΔH [mJ/mg] derived from melting of the release agent per 1 mg of toner was obtained.

[Measurement of storage modulus]
0.1 g of toner was set in a pellet molding machine, and a pressure of 5 MPa was applied to the toner to obtain cylindrical pellets having a diameter of 10 mm and a thickness of 1.2 mm. Subsequently, the obtained pellets were set in the measuring device. As a measuring device, a rheometer ("Physica MCR-301" manufactured by Anton Paar) was used. A measuring jig (parallel plate) was attached to the tip of the shaft of the measuring device (more specifically, the shaft driven by a motor). The pellet was placed on a plate of the measuring device (specifically, a heat table heated by a heater). The pellets on the plate were heated to 110° C. to melt the pellets (toner lumps) once. When the entire pellet is melted, a measuring jig (parallel plate) is brought into close contact with the melted toner, and the toner is sandwiched between two parallel plates (upper: measuring jig, lower: heat table). . Then, the toner was cooled to 40°C. After that, using a measuring device, the measurement temperature range is 40 ° C. to 200 ° C., the temperature increase rate is 4 ° C./min, the vibration frequency is 1 Hz, and the strain is 1% (however, in the measurement temperature range of 40 ° C. to 100 ° C., the strain is 0.01%. ~1%), the G' temperature dependency curve (vertical axis: storage modulus, horizontal axis: temperature) was measured. Then, the temperature at a storage elastic modulus of 10 ⁸ Pa and the temperature at a storage elastic modulus of 10 ⁵ Pa were read from the obtained storage elastic modulus temperature dependence curve.

In Table 2 below, "unopened ring OX group [μmol/g]" indicates the content ratio of the unopened ring oxazoline group in each toner. The "10 ⁵ Pa temperature" and "10 ⁸ Pa temperature" in the storage elastic modulus are the temperature at which the storage elastic modulus is 1.0×10 ⁵ Pa and the temperature at which the storage elastic modulus is 1.0× in measurement of the toner with a rheometer. and the temperature at which the pressure becomes 10 ⁸ Pa, respectively. In Toner (B-9), "-" in the saturation magnetization and shape of the magnetic powder indicates that the corresponding item was not measured or observed. The amount of magnetic powder added in the toner (B-7) indicates that the magnetic powder was internally added to the toner core and the content of the magnetic powder in the toner core was 0.5% by mass.

<Evaluation>
Heat-resistant storage stability, low-temperature fixability (minimum fixation temperature), color development, and Adhesion to the photosensitive drum was evaluated. The evaluation results are shown in Table 3 below.

[Heat resistant storage stability]
3 g of an object to be evaluated (one of toners (A-1) to (A-9) and toners (B-1) to (B-9)) was placed in a polyethylene container having a capacity of 20 mL. This polyethylene container was allowed to stand in a thermostat set at 60° C. for 3 hours. Thereafter, the polyethylene container was taken out from the thermostat, and the toner in the polyethylene container was cooled at 20° C. for 3 hours to obtain the heat-treated toner.

Subsequently, the heat-treated toner was placed on a 100-mesh (150 μm opening) sieve with a known mass. Then, the total mass of the toner and the sieve was measured, and the mass of the toner on the sieve (the mass of the toner before sieving) was calculated from the measurement results. Subsequently, the sieve is set in a powder property evaluation device ("Powder Tester (registered trademark) PT-X" manufactured by Hosokawa Micron Corporation), and the amplitude is 1.0 mm for 30 seconds according to the manual of the powder property evaluation device. The sieve was vibrated to screen out the toner. After sieving, the total mass of the toner and the sieve was measured, and the mass of the toner remaining on the sieve (the mass of the toner after sieving) was calculated from the measurement result. From the mass of the toner before sieving and the mass of the toner after sieving, the cohesion rate [% by mass] was calculated according to the following formula.
Aggregation rate = 100 x mass of toner after sieving/mass of toner before sieving

The heat-resistant storage stability of the toner can be evaluated as "good" when the aggregation rate is less than 10% by mass, and can be evaluated as "poor" when the aggregation rate is 10% by mass or more.

(Preparation of developer for evaluation)
An evaluation developer used for evaluation of low-temperature fixability, glossiness and colorimetry was prepared by the following method. Under an environment of temperature 23 ° C. and humidity 50% RH, 100 parts by mass of developer carrier (carrier for "FS-C5250DN" manufactured by Kyocera Document Solutions Co., Ltd.) and evaluation objects (toner (A-1) to (A- 9) and 10 parts by mass of toners (B-1) to (B-9) were mixed for 30 minutes using a ball mill to obtain an evaluation developer (two-component developer).

[Low temperature fixability]
An image was formed using the evaluation developer (two-component developer) prepared as described above, and the low-temperature fixability (minimum fixation temperature) was evaluated. As an evaluation machine, a printer equipped with a Roller-Roller type heating and pressurizing fixing device (Kyocera Document Solutions Co., Ltd. "FS-C5250DN" was modified to enable the fixing temperature to be changed) was used. The developer for evaluation (developer containing any of toners (A-1) to (A-9) and (B-1) to (B-9)) is put into the black developing device of the evaluation machine and replenished. A toner for black (the same toner as the toner contained in the developer for evaluation) was put into the black toner container of the evaluation machine.

Using the above evaluation machine, under the conditions of a temperature of 32.5° C. and a humidity of 80% RH, on A4 size printing paper (basis weight: 90 g/m ² ), under the conditions of a toner amount of 1.0 mg/cm ² , A solid image (more specifically, an unfixed toner image) was formed. Subsequently, the printing paper (evaluation paper) on which the solid image was formed was passed through the fixing device of the evaluation machine.

In the evaluation of low-temperature fixability, the fixing temperature was measured in a range of 90° C. or higher and 120° C. or lower. Specifically, the fixing temperature of the fixing device was raised from 90° C. by 1° C., and the lowest temperature (minimum fixing temperature) at which a solid image (unfixed toner image) could be fixed on paper was measured. Whether or not the unfixed toner image could be fixed was confirmed by the following fold rubbing test.

The evaluation paper passed through the fixing device was folded so that the surface on which the solid image was formed faces the inside. More specifically, the evaluation sheet was folded so that the folding line passed through approximately the center of the solid image. The folded evaluation paper was rubbed back and forth on the crease using a fabric-coated 1 kg weight with no force applied from above. After that, the evaluation paper was unfolded, and the length of toner peeling (peeling length) at the portion where the solid image was fixed in the folded portion of the evaluation paper was measured. When the peeling length was 1 mm or less, it was determined that the unfixed toner image could be fixed.

Low-temperature fixability can be evaluated as "good" when the minimum fixing temperature is 105°C or less, and can be evaluated as "poor" when the minimum fixing temperature is over 105°C.

[Color development]
(gross)
A solid image (more specifically, an unfixed toner image) was formed on printing paper by the same method as described in the evaluation of low-temperature fixability. Subsequently, the printing paper (evaluation paper) on which the solid image was formed was passed through the fixing device of the evaluation machine. The fixing temperature was 130°C. Then, using a handy gloss meter (“Gloss Checker IG-331” manufactured by Horiba, Ltd.), the gloss value of the solid image after fixing was measured at a measurement angle of 60°.

(colorimetry)
Using the same evaluator as that used in the evaluation of the low-temperature fixability, under the environment of a temperature of 23° C. and a humidity of 50% RH, an A4 size printing paper (basis weight: 70 g/m ² ) was subjected to a toner loading amount of 0.00. A 45 mm×45 mm solid image (more specifically, an unfixed toner image) was formed under the condition of 4 mg/cm ² . Subsequently, the printing paper (evaluation paper) on which the solid image was formed was passed through the fixing device of the evaluation machine. The fixing temperature is 120° C., 130° C. or 140° C. for toners (A-1) and (B-8). For (B-7) and (B-9), one set of 130°C was used. The solid image after fixing was measured by a colorimeter ("SpectroEye (registered trademark)" manufactured by GretagMacbeth).

For each toner, when the gloss value is 7 or more and 15 or less, and the colorimetry result is "L* is 20 or less, a* is -3 or more and 0 or less, and b* is -4 or more and 0 or less", the black toner is defined as " Otherwise, it can be evaluated as "bad" as a black toner. An image with "L* of 20 or less, a* of -3 or more and 0 or less, and b* of -4 or more and 0 or less" tends to be perceived as the most natural black by human eyes.

[Adhesion to photoreceptor drum]
An evaluation developer used for evaluation of adhesion of toner to a photoreceptor drum was prepared by the following method. In an environment of temperature 23° C. and humidity 50% RH, 100 parts by mass of a developer carrier (carrier for “FS-C5300DN” manufactured by Kyocera Document Solutions Co., Ltd.) and an evaluation object (toner (A-1) to (A- 9) and 10 parts by mass of toners (B-1) to (B-9) were mixed for 30 minutes using a ball mill to obtain an evaluation developer (two-component developer).

Using the developer for evaluation (two-component developer) prepared as described above, adhesion of toner to the photosensitive drum was evaluated. As an evaluation machine, a printer (“FS-C5300DN” manufactured by Kyocera Document Solutions Co., Ltd.) equipped with a roller-roller heat-pressure fixing device was used. The developer for evaluation (developer containing any of toners (A-1) to (A-9) and (B-1) to (B-9)) is put into the black developing device of the evaluation machine and replenished. A toner for black (the same toner as the toner contained in the developer for evaluation) was put into the black toner container of the evaluation machine. After that, the evaluator was allowed to stand still for 24 hours.

Continuous printing of 50,000 sheets was performed at a printing rate of 5% under an environment of temperature of 23° C. and humidity of 50% RH. A4 size printing paper (basis weight: 70 g/m ² ) was used as the recording medium. After that, the photoreceptor drum was taken out from the evaluation machine and visually observed to confirm whether or not toner adhered to the surface of the photoreceptor drum.

Toners (A-1) to (A-9) of Examples each contained toner particles. The toner particles comprise a toner core containing a release agent having a carboxyl group, a shell layer partially covering the surface of the toner core, and magnetic particles adhering to portions of the surface of the toner core that are not covered with the shell layer. I was prepared. At least part of the surface of the magnetic particles was exposed from the shell layer, and protruded radially outward of the toner core from the surface of the shell layer. The content of the magnetic particles was 0.1 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the toner core. The shell layer contained a shell resin with unopened oxazoline groups. The content of unopened oxazoline groups measured by gas chromatography-mass spectrometry was 490 μmol/g or more and 1,500 μmol/g or less. In measurement by differential scanning calorimetry, the endothermic amount derived from melting of the release agent was 80 mJ/mg or more and 160 mJ/mg or less. As shown in Table 3, toners (A-1) to (A-9) were all excellent in heat-resistant storage stability, low-temperature fixability and color development, and were able to suppress adhesion to the photoreceptor drum. In addition, the toner (A-1) was excellent in color development at any fixing temperature of 120.degree. C., 130.degree. C. and 140.degree.

On the other hand, toners (B-1) to (B-9) of Comparative Examples did not have the above-described structure. Specifically, toners (B-1) and (B-3) each contained less than 490 μmol/g or more than 1,500 μmol/g of unopened oxazoline groups. Toners (B-2) and (B-4) each had an endothermic amount of less than 80 mJ/mg or more than 160 mJ/mg due to melting of the release agent. Toners (B-5) and (B-6) contained less than 0.1 parts by weight or more than 1.5 parts by weight of the magnetic powder with respect to 100 parts by weight of the toner core. In the toner (B-7), the magnetic particles were internally added to the toner core, and no magnetic particles adhered to the surface of the toner core. Toners (B-8) and (B-9) did not contain magnetic particles or contained titanium oxide powder instead of magnetic particles. As a result, the toners (B-1) to (B-9) were found to be poor in at least one of heat-resistant storage stability, low-temperature fixability, and color development, or could not be prevented from adhering to the photoreceptor drum.

The titanium oxide particles used as an external additive in the toners (A-1) to (A-9) of the examples and the toners (B-1) to (B-9) of the comparative examples have an effect on the color developability of the toner. had no effect. This is because the titanium oxide particles used as the external additive are separated from the toner particles when the toner image is developed on the photoreceptor, and remain on the photoreceptor when the toner image is transferred to the recording medium. In other words, the titanium oxide particles externally added to the toner particles did not affect the color developability of the toner because they were not transferred to the recording medium.

A black toner according to one embodiment of the present invention can be used, for example, to form images in copiers, printers, or multifunction devices.

REFERENCE SIGNS LIST 1 toner particle 11 toner core 12 shell layer 13 magnetic particle S endothermic peak derived from melting of release agent

Claims (7)

A black toner comprising toner particles,
The toner particles are
a toner core containing a release agent having a carboxy group;
a shell layer partially covering the surface of the toner core;
Magnetic particles attached to a portion of the surface of the toner core that is not covered with the shell layer;
At least part of the surface of the magnetic particles is exposed from the shell layer and protrudes radially outward of the toner core from the surface of the shell layer,
The content of the magnetic particles is 0.1 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the toner core,
The shell layer contains a shell resin having an unopened ring oxazoline group,
The content of unopened oxazoline groups measured by gas chromatography-mass spectrometry is 490 μmol/g or more and 1,500 μmol/g or less,
A black toner, wherein, as measured by differential scanning calorimetry, an endothermic amount derived from melting of the release agent is 80 mJ/mg or more and 160 mJ/mg or less. 2. The black toner according to claim 1, wherein the releasing agent is an ester wax having a carboxy group. 3. The black toner according to claim 1, wherein a content of said release agent in said toner core is 60% by mass or more and 95% by mass or less. 4. The black toner according to claim 3, wherein the content of the binder resin in the toner core is 15% by mass or less. The temperature at which the storage modulus becomes 1.0×10 ⁸ Pa is 70° C. or higher,
5. The black toner according to claim 1, wherein the temperature at which the storage elastic modulus becomes 1.0×10 ⁵ Pa is 85° C. or less. The black toner according to any one of claims 1 to 5, wherein the shell resin has a repeating unit represented by the following general formula (I) and a repeating unit represented by the following general formula (II). .

(In the general formula (I), R ¹ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms which may be substituted with a phenyl group,
In the general formula (II), R ² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms which may be substituted with a phenyl group, and * represents an atom contained in the release agent. represents the binding site of ) 7. The black toner according to claim 6, wherein the shell resin further has a repeating unit represented by general formula (III) below.

(In general formula (III), R ³ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms which may be substituted with a phenyl group, and R ⁴ represents 1 to 3 carbon atoms. represents the alkyl group of.)

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