JP2016126075A - Electrostatic latent image development toner and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic latent image development toner excellent in color development, heat-resistant storage, charge stability, and image density stability.SOLUTION: An electrostatic latent image development toner includes a plurality of toner particles. The toner particles include a toner core containing a binder resin and a colorant, and a shell layer that covers the toner core. The shell layer contains a thermosetting resin and a thermoplastic resin. The thermosetting resin is at least one resin selected from an amino resin group consisting of a melamine resin, an urea resin, and a glyoxal resin. The thickness of the shell layer is 5 nm or more and 50 nm or less. As the binder resin, a crystalline resin and an amorphous resin are contained. The melting point of the crystalline resin is 50°C or more and 100°C or less. As the colorant, a black colorant and a color gamut conditioner are contained.SELECTED DRAWING: Figure 1

Description

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

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

  Therefore, for the purpose of obtaining a toner excellent in fixability even in a low temperature range, for the purpose of improving the storage stability of the toner at a high temperature, and for the purpose of improving the blocking resistance of the toner, a toner particle having a core-shell structure is included. Toner is used. The toner particles having a core-shell structure include a toner core and a shell layer that covers the toner core. In an example of toner particles having a core-shell structure, the toner core includes a binder resin having a low melting point. The shell layer is made of a resin having a glass transition point higher than that of the binder resin contained in the toner core.

  As an example of a toner containing toner particles having a core-shell structure, the following toner has been proposed (Patent Document 1). In this toner, the surface of the toner core is substantially continuously covered with a thin film (shell layer). The thin film (shell layer) contains a thermosetting resin. The softening temperature of the toner core before coating is 40 ° C. or higher and 150 ° C. or lower.

  Further, a toner containing carbon black and an inorganic blue pigment has been proposed (Patent Document 2). Furthermore, a color image forming method using four types of toners, yellow toner, magenta toner, cyan toner, and black toner has been proposed (Patent Document 3). For black toner, carbon black and C.I. I. Pigment Blue (15: 1, 15: 2, or 15: 3) is included.

JP 2004-138985 A JP-A-4-182672 JP 2009-301026 A

However, the toner described in Patent Document 1 is not sufficient in terms of charging stability and color developability (for example, L ^* value, a ^* value, and b ^* value) of the formed image. Furthermore, since the shell layer is formed of a thermosetting resin, it is not necessarily fixed well at a low temperature. Therefore, when trying to form an image with a high fixing temperature, there is a problem that the melted toner particles are easily fused to the heated fixing roller, and the formed image is likely to be offset.

Further, the toner described in Patent Document 2 is not yet sufficiently stable in charging stability. Further, the toner described in Patent Document 2 is not sufficient in terms of heat-resistant storage stability and color developability (for example, L ^* value, a ^* value, and b ^* value) of an image to be formed. Furthermore, it is difficult to use this technique for toners that include toner particles that melt at low temperatures, which have been developed in recent years.

The toner described in Patent Document 3 uses only an amorphous (non-crystalline) polyester resin for forming a coating layer (shell layer). Therefore, the heat resistant storage stability of the toner is not sufficient. The toner described in Patent Document 3 is intended to improve the image quality of a color image, and is not sufficient in terms of color developability (for example, L ^* value, a ^* value, and b ^* value) of a black toner. Furthermore, in the toner described in Patent Document 3, the thickness of the coating layer (shell layer) is preferably 20 nm or more and 500 nm or less. However, when the shell layer is formed of an amorphous polyester resin, in actual use of such a toner, filming due to the amorphous polyester is likely to occur when the thickness of the shell layer is 20 nm to 300 nm. Become. Further, when the thickness of the shell layer exceeds 300 nm, the low-temperature fixability of the toner tends to be remarkably lowered. When the low-temperature fixability of the toner is lowered, the temperature region where no toner offset occurs is reduced. Therefore, when the shell layer is formed only from the amorphous polyester resin, it is difficult to improve the low-temperature fixability of the toner while suppressing the filming of the toner.

  The present invention has been made in view of the above problems, and an object thereof is to provide a toner for developing an electrostatic latent image, which is excellent in color developability, heat-resistant storage stability, charge stability, and image density stability. To do. Another object of the present invention is to provide an image forming method capable of forming an image having excellent color developability and stability of image density.

  The electrostatic latent image developing toner of the present invention includes a plurality of toner particles. The toner particles include a toner core including a binder resin and a colorant, and a shell layer that covers the toner core. The shell layer includes a thermosetting resin and a thermoplastic resin. The thermosetting resin is at least one resin selected from the amino resin group consisting of melamine resin, urea resin, and glyoxal resin. The shell layer has a thickness of 5 nm to 50 nm. The binder resin includes a crystalline resin and an amorphous resin. The melting point of the crystalline resin is 50 ° C. or higher and 100 ° C. or lower. As the colorant, a black colorant and a color gamut adjusting agent are included.

The image forming method of the present invention is a method of forming an image using the above-described toner for developing an electrostatic latent image. The image forming method of the present invention includes a transfer step and a fixing step. In the transfer step, a transfer bias is applied to the recording medium so that the amount of the electrostatic latent image developing toner placed on the recording medium is 0.4 mg / cm ² . In the fixing step, the electrostatic latent image developing toner is fixed on the recording medium. The a ^* value of the formed image is -4 or more and 1 or less, the b ^* value is -4 or more and 1 or less, and the L ^* value is 22 or less.

  According to the present invention, it is possible to provide a toner for developing an electrostatic latent image that is excellent in color developability, heat-resistant storage stability, charging stability, and image density stability. According to the image forming method of the present invention, an image having excellent color developability and stability of image density can be formed.

It is the schematic which shows the structure of the image forming apparatus used for the image forming method of 2nd embodiment.

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

<First Embodiment: Electrostatic latent image developing toner>
The first embodiment relates to an electrostatic latent image developing toner (hereinafter sometimes referred to as “toner”).

  The toner of the present embodiment includes a plurality of toner particles. The toner particles include a toner core and a shell layer that covers the toner core. The shell layer is formed (positioned) on the surface of the toner core so as to cover the toner core. The toner may substantially contain only toner particles, or may contain components other than toner particles in addition to the toner particles.

  An external additive may be attached to the toner core covered with the shell layer as necessary. Hereinafter, the toner core covered with the shell layer before the external additive is adhered may be referred to as toner base particles.

  Further, the toner can be mixed with a desired carrier and used as a two-component developer.

  Hereinafter, the toner core and the shell layer included in the toner particles will be described. Further, an external additive which is an optional component, a carrier used when a toner is used in a two-component developer, and a method for producing the toner will be described.

<1. Toner core>
The toner core includes a binder resin and a colorant. The toner core may further contain a release agent, a charge control agent, and / or a magnetic powder as necessary. Hereinafter, the binder resin and the colorant contained in the toner core will be described. In addition, a release agent, a charge control agent, and magnetic powder, which may be included in the toner core as necessary, will be described.

<1-1. Binder resin>
The toner core includes a crystalline resin and an amorphous resin as a binder resin. When the toner core contains the crystalline resin in addition to the amorphous resin, the initial charge amount of the obtained toner and the decrease in the charge amount of the toner after continuous printing tend to be suppressed. In other words, such a toner tends to be excellent in charging stability (durability stability in charging). As a result, the image density of an image formed using toner tends to be a suitable value. Further, even when continuous printing is performed, a decrease in image density of the formed image tends to be suppressed. In other words, such a toner tends to be excellent in image density stability (durability stability at image density). Furthermore, the occurrence of fogging of toner on the recording medium during image formation tends to be suppressed. Further, a toner containing toner particles prepared using a toner core containing a crystalline resin has excellent low-temperature fixability, and tends to particularly suppress the occurrence of offset when fixing the toner to a recording medium at a high temperature.

  As the crystalline resin, for example, a resin having a crystallization index of 0.90 or more and less than 1.10 can be used. In order to improve charging stability and image density stability, it is preferable to use a crystalline resin having a crystallinity index of 0.98 to 1.05. As the non-crystalline resin, for example, a resin having a crystallization index of less than 0.90, or 1.10 or more can be used. In order to improve the charging stability of the toner and the stability of the image density of the formed image, it is preferable to use an amorphous resin having a crystallinity index of less than 0.98 or more than 1.05. . In addition, the kind of resin which can be used as a crystalline resin and an amorphous resin is mentioned later.

  The crystallinity index of the crystalline resin and the resin used as the non-crystalline resin is a ratio (Tm) between the softening point (Tm) of the resin and the melting point of the resin (the temperature of the maximum endothermic peak in the DSC curve, Mp). / Mp). The softening point (Tm) of the resin and the melting point (Mp) of the resin can be measured by the same method as the softening point (Tma) of the amorphous resin and the melting point (Mpc) of the crystalline resin described later.

  The melting point (Mpc) of the crystalline resin is 50 ° C. or higher and 100 ° C. or lower. A toner containing toner particles prepared using a toner core containing a crystalline resin having a melting point (Mpc) in such a range is excellent in heat storage stability and low-temperature fixability, and is offset when fixing at high temperature. It is thought that the occurrence of stagnation can be particularly suppressed. The melting point (Mpc) of the crystalline resin is measured using, for example, a differential scanning calorimeter. Below, an example of the measuring method of melting | fusing point (Mpc) of crystalline resin is demonstrated.

(Measuring method of melting point)
The melting point (Mpc) of the crystalline resin as the binder resin is measured using a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.). After putting a crystalline resin sample of 10 mg or more and 20 mg or less into an aluminum dish, the aluminum dish is set in the measuring part of the DSC. Use an empty aluminum pan for reference. The temperature is increased to 170 ° C. at a rate of 10 ° C./min with 30 ° C. as the measurement start temperature. The maximum peak temperature of the heat of fusion observed during the temperature rise is defined as the melting point (Mpc) of the crystalline resin.

(Measurement method of glass transition point)
The glass transition point (Tga) of the amorphous resin as the binder resin is preferably 30 ° C. or higher and 60 ° C. or lower, and more preferably 35 ° C. or higher and 55 ° C. or lower. The glass transition point (Tga) of the amorphous resin can be measured according to the following method.

  The glass transition point (Tga) of the amorphous resin can be determined from the change point of the specific heat of the amorphous resin using a differential scanning calorimeter (DSC). More specifically, a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.) was used as a measuring device. The glass transition point (Tga) of the amorphous resin can be obtained by measuring the endothermic curve of the amorphous resin. 10 mg of a sample (non-crystalline resin) is put in an aluminum pan, and an empty aluminum pan is used as a reference. Obtaining the glass transition point (Tga) of the amorphous resin from the endothermic curve of the amorphous resin obtained by measurement under the conditions of a measurement temperature range of 25 ° C. to 200 ° C. and a temperature increase rate of 10 ° C./min. Can do.

  The softening point (Tma) of the non-crystalline resin as the binder resin is preferably 60 ° C. or higher and 150 ° C. or lower, and more preferably 70 ° C. or higher and 140 ° C. or lower. Also, a plurality of types of amorphous resins having different softening points (Tma) can be used in combination so that the softening point of the entire binder resin is in such a range. The softening point (Tma) of the amorphous resin can be measured according to the following method.

(Measurement method of softening point)
The softening point (Tma) of the amorphous resin is measured using a Koka flow tester (for example, “CFT-500D” manufactured by Shimadzu Corporation). A sample (non-crystalline resin) is set in the Koka flow tester. A 1 cm ³ sample is melted and discharged under the conditions of a die pore diameter of 1 mm, a plunger load of 20 kg / cm ² , and a heating rate of 6 ° C./min. Thereby, the softening point (Tma) is measured. The softening point (Tma) of the amorphous resin is read from an S-shaped curve with respect to temperature (° C.) / Stroke (mm) obtained by measurement with the Koka flow tester. Specifically, the maximum value of the stroke and S _1, the stroke value of the low-temperature side of the base line and S _2. The temperature at which the stroke value in the S-shaped curve is (S ₁ + S ₂ ) / 2 is defined as the softening point (Tma) of the sample. Note that the softening point (Tma) of the sample corresponds to a half outflow temperature (T1 / 2) of the amorphous resin.

  The ratio (P / Q) of the mass (P) of the crystalline resin in the binder resin and the mass (Q) of the resin (non-crystalline resin) excluding the crystalline resin is preferably 1 or less. 1/99 or more and 50/50 or less is more preferable, 5/95 or more and 30/70 or less is more preferable, and 10/90 or more and 20/80 or less is particularly preferable.

  The total content of the crystalline resin and the amorphous resin in the binder resin is preferably 70% by mass or more, more preferably 80% by mass or more, based on the mass of the binder resin. More preferably, it is 90 mass% or more, and it is especially preferable that it is 100 mass%.

  The mass average molecular weight (Mw) of the binder resin is preferably 10,000 or more and 50,000 or less. The molecular weight distribution (Mw / Mn) of the binder resin, which is represented by the ratio between the weight average molecular weight (Mw) of the binder resin and the number average molecular weight (Mn), is preferably 8 or more and 50 or less. When the toner core includes a binder resin having such a weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn), the toner including toner particles prepared using such a toner core is heat-resistant. And low temperature fixability, and even when the toner is fixed at a high temperature, the occurrence of toner offset tends to be suppressed.

  When the toner core includes a binder resin having a mass average molecular weight (Mw) that is too low, when an image is formed using toner including toner particles having such a toner core, the toner offset may occur when the toner is fixed at a high temperature. May occur. When the toner core contains a binder resin having a mass average molecular weight (Mw) that is too high, when the image is formed using toner containing toner particles having such a toner core, the toner is good when the toner is fixed at a low temperature. May not be fixed.

  When the toner core contains a binder resin having a molecular weight distribution (Mw / Mn) that is too small, when an image is formed using toner containing toner particles having such a toner core, the toner offset is fixed when the toner is fixed at a high temperature. May occur. When the toner core contains a binder resin having a molecular weight distribution (Mw / Mn) that is too large, when an image is formed using toner containing toner particles having such a toner core, the toner is fixed when the toner is fixed at a low temperature. It may not be fixed well.

  The mass average molecular weight (Mw) and the number average molecular weight (Mn) of the binder resin can be measured using gel permeation chromatography (GPC). Hereinafter, an example of a molecular weight measurement method using GPC will be described.

(Measurement method of molecular weight using GPC)
Tetrahydrofuran (THF) is used as the solvent. The sample is put into THF so that the concentration of the sample (binder resin) is 3.0 mg / mL. Subsequently, the obtained mixed solution is allowed to stand for 1 hour to dissolve the sample in THF. The obtained THF solution is filtered using a sample pretreatment filter (“Chromatodisc 25N”, Kurashiki Boseki Co., Ltd., non-aqueous, membrane pore size 0.45 μm), and the liquid that has passed through the filter is used as a sample solution. The measurement of GPC is performed, for example, with an apparatus and conditions described later. Specifically, the column is stabilized in a heat chamber at a predetermined temperature (for example, 40 ° C.). Subsequently, THF as a solvent is caused to flow through the column at a predetermined temperature (for example, 40 ° C.) (for example, a flow rate of 1 mL / min), and a GPC sample (for example, 50 μL or more and 200 μL or less) is introduced into the column. Then, the molecular weight distribution of the GPC sample introduced into the column is measured.

The molecular weight distribution is calculated from the relationship between the logarithmic value of a calibration curve prepared from a monodisperse polystyrene standard sample and the number of counts (retention time). As a standard polystyrene sample for preparing a calibration curve, for example, a sample having a molecular weight of about 1 × 10 ³ or more and 1 × 10 ⁷ or less is used. Examples of commercially available standard polystyrene samples for preparing a calibration curve include samples manufactured by Tosoh Corporation (molecular weight: 3.84 × 10 ⁶ , 1.09 × 10 ⁶ , 3.55 × 10 ⁵ , 1.02 × 10 ⁵ , 4.39 × 10 ⁴ , 9.10 × 10 ³ , and 2.98 × 10 ³ ). In the molecular weight distribution measurement of the polyester resin, several types (for example, at least about 7 points) of standard polystyrene samples are used. For example, an RI (refractive index) detector is used as the detector. As the column, it is preferable to use a combination of a plurality of commercially available polystyrene gel columns in order to accurately measure a molecular weight region of 1 × 10 ³ or more and 2 × 10 ⁶ or less.

(GPC measurement conditions)
Apparatus: HLC-8220 (manufactured by Tosoh Corporation)
Eluent: THF (tetrahydrofuran)
Column: TSKgel GMHXL (manufactured by Tosoh Corporation)
Number of columns: 2 Detector: RI
Eluent flow rate: 1 mL / min Sample solution concentration: 3.0 mg / mL
Column temperature: 40 ° C
Sample solution volume: 100 μL
Calibration curve: prepared using standard polystyrene

  The type of resin used for the crystalline resin and the amorphous resin is not particularly limited as long as it is a binder resin used for toner preparation. As the kind of the resin used for the crystalline resin and the non-crystalline resin, a thermoplastic resin is preferable from the viewpoint of improving the fixability of the toner. Examples of the thermoplastic resin include acrylic resins, styrene acrylic resins, polyester resins, polyamide resins, urethane resins, and polyvinyl alcohol resins. In order to improve the dispersibility of the colorant in the toner core, the chargeability of the toner particles, and the fixability of the toner to the recording medium (for example, paper), a polyester resin is particularly preferable.

  When the toner core contains a polyester resin, a toner containing toner particles in which the shell layer and the toner core are firmly bonded tends to be obtained. The reason is presumed as follows. As described later, the toner particles contained in the toner are obtained by curing the raw material of the shell layer (for example, a monomer or prepolymer of a thermosetting resin, and a thermoplastic resin) and covering the surface of the toner core with the shell layer. Prepared by When the toner core contains a polyester resin, a functional group (for example, a hydroxyl group or a carboxyl group) that can react with the monomer or prepolymer of the thermosetting resin that the polyester resin has is exposed on the surface of the toner core. Therefore, when the toner core is coated with the shell layer, the monomer or prepolymer (for example, methylol melamine) of the thermosetting resin reacts with the functional group (for example, hydroxyl group or carboxyl group) exposed on the surface of the toner core. Thus, it is considered that a covalent bond is formed between the toner core and the shell layer. As a result, a toner containing toner particles in which the shell layer and the toner core are firmly bonded tends to be obtained.

  Hereinafter, the polyester resin when the polyester resin is used as the crystalline resin and the non-crystalline resin will be described.

  The polyester resin can be appropriately selected from polyester resins used as a binder resin for toner. The polyester resin can be obtained by, for example, condensation polymerization or co-condensation polymerization of alcohol and carboxylic acid. As a component used when synthesize | combining a polyester resin, the following alcohol and carboxylic acid are preferable, for example.

  Examples of the alcohol used when synthesizing the polyester resin include dihydric alcohols and trihydric or higher alcohols.

  Specific examples of the dihydric alcohol used when synthesizing the polyester resin include diols and bisphenols. Examples of the diol include aliphatic diols having 2 to 10 carbon atoms, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Examples of bisphenols include bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, and polyoxypropylenated bisphenol A. Examples of the aliphatic diol having 2 to 10 carbon atoms include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, Examples include 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, and dipropylene glycol.

  Specific examples of trihydric or higher alcohols used for synthesizing polyester resins 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, trimethylolpropane And 1,3,5-trihydroxymethylbenzene.

  Examples of the carboxylic acid used when synthesizing the polyester resin include divalent carboxylic acids and trivalent or higher carboxylic acids.

  Specific examples of the divalent carboxylic acid used for synthesizing the polyester resin include aliphatic divalent carboxylic acids having 2 to 16 carbon atoms, phthalic acid, isophthalic acid, and terephthalic acid. Examples of the aliphatic divalent carboxylic acid having 2 to 16 carbon atoms include alkane dicarboxylic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, cyclohexanedicarboxylic acid having 2 to 16 carbon atoms, Examples include adipic acid, sebacic acid, azelaic acid, malonic acid, succinic acid, alkyl succinic acid, and alkenyl succinic acid. More specifically, examples of the alkyl succinic acid include n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, and isododecyl succinic acid. More specific examples of the alkenyl succinic acid include n-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, and isododecenyl succinic acid.

  Specific examples of the trivalent or higher carboxylic acid used for synthesizing the polyester resin include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2,5,5, 7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylene Examples include carboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empol trimer acid.

  The above-mentioned alcohol and carboxylic acid may be used individually by 1 type, respectively, and may be used in combination of 2 or more type. Furthermore, the above divalent or trivalent or higher carboxylic acid may be derivatized to an ester-forming derivative such as an acid halide, an acid anhydride, or a lower alkyl ester. Here, “lower alkyl” means an alkyl group having 1 to 6 carbon atoms.

  The crystallinity index of the polyester resin can be adjusted by appropriately adjusting the type and amount of alcohol used as a monomer, and the type and amount of carboxylic acid. Crystalline polyester may be used independently and may be used in combination of 2 or more type.

  Among the alcohols used in the synthesis of the polyester resin, aliphatic diols having 2 to 10 carbon atoms are preferred, and aliphatics having 2 to 8 carbon atoms are preferred because they facilitate the crystallization of the polyester resin. Diols are more preferred. Of these, α, ω-alkanediols having 2 to 8 carbon atoms are more preferred because they facilitate the crystallization of the polyester resin.

  In order to obtain a crystalline polyester resin, the content of an aliphatic diol having 2 to 10 carbon atoms is 80 mol% or more based on the number of moles of alcohol used when synthesizing the polyester resin. Is preferable, and it is more preferable that it is 90 mol% or more. In order to obtain a crystalline polyester resin, the content of the component (single compound) contained in the largest amount in the alcohol used when synthesizing the polyester resin is preferably 70 mol% or more, More preferably, it is 90 mol% or more, and most preferably 100 mol%.

  Among the carboxylic acids used when synthesizing the polyester resin, aliphatic divalent carboxylic acids (dicarboxylic acids) having 2 to 16 carbon atoms are preferable because the crystallization of the polyester resin is facilitated. An α, ω-alkanedicarboxylic acid having a number of 2 or more and 16 or less (for example, 1,10-decanedicarboxylic acid) is more preferable.

  In order to obtain a crystalline polyester resin, the content of the aliphatic dicarboxylic acid having 2 to 16 carbon atoms is 70 mol% or more with respect to the number of moles of carboxylic acid used for synthesizing the polyester resin. It is preferable that it is 90 mol% or more. In order to obtain a crystalline polyester resin, the content of the component (single compound) contained in the largest amount in the carboxylic acid is preferably 70 mol% or more, more preferably 90 mol% or more. Preferably, it is 100 mol%, and most preferably.

  The acid value of the polyester resin is preferably 5 mgKOH / g or more and 30 mgKOH / g or less. The hydroxyl value of the polyester resin is preferably 15 mgKOH / g or more and 80 mgKOH / g or less.

  The acid value and the hydroxyl value of the polyester resin are appropriately changed depending on the amount of divalent or trivalent or higher alcohol used and the amount of divalent or trivalent or higher carboxylic acid used when the polyester resin is produced. Can be adjusted. Moreover, when the molecular weight of the polyester resin is increased, the acid value and hydroxyl value of the polyester resin tend to decrease.

  When polyester is used as the binder resin, the toner core may further contain another thermoplastic resin as the binder resin in addition to the polyester resin. Further, another thermoplastic resin that may be included is appropriately selected from thermoplastic resins conventionally used as a binder resin for toner.

  When a crystalline polyester resin and an amorphous polyester resin are used as the binder resin, the content of the polyester resin in the binder resin (the total content of the crystalline polyester resin and the amorphous polyester resin) is: It is preferably 70% by mass or more, more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass.

<1-2. Colorant>
The toner core includes a black colorant and a color gamut adjusting agent as a colorant. When the toner core includes a black colorant and a color gamut adjusting agent, an image formed using a toner including toner particles having such a toner core has color developability (for example, L ^* value, a ^* value, and b ^* value) tends to be excellent.

  Examples of the black colorant include black pigments and black dyes. Examples of the black pigment include carbon black. As the black colorant, it is also possible to use a colorant that is toned to black using one or more of known yellow colorants, magenta colorants, and cyan colorants. As the black colorant, a black pigment is preferable, and carbon black is more preferable.

When the toner core includes a color gamut adjusting agent, the color gamut of the formed image (for example, a range of L ^* value, a ^* value, and b ^* value) can be easily adjusted to a desired range. Preferably, the color gamut adjusting agent includes a cyan colorant (specifically, a cyan pigment and a cyan dye). Examples of cyan colorants include copper phthalocyanine compounds, copper phthalocyanine derivatives, anthraquinone compounds, and basic dye lake compounds. Specific 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, C.I. I. Acid blue and “Violet BL” (manufactured by Nippon Chemical Industry Co., Ltd.) can be mentioned. Of these, C.I. I. Pigment Blue (15: 2, or 15: 3), or “Violet BL” (manufactured by Nippon Chemical Industry Co., Ltd.).

Here, when the loading amount of the toner of this embodiment onto the recording medium is 0.4 mg / cm ² , the a ^* value of the image formed by fixing the toner on the recording medium is −4 or more and 1 It is preferable that the b ^* value is -4 or more and 1 or less and the L ^* value is 22 or less. The L ^* value, a ^* value, and b ^* value are values in the CIE 1976 (L ^* , a ^* , b ^* ) color space. The L ^* value, a ^* value, and b ^* value can be measured using, for example, a Macbeth reflection densitometer (“SpectroEye” manufactured by Sakata Inx Engineering Co., Ltd.). The toner can be fixed on the recording medium using, for example, a color printer (“FS-C5300DN” manufactured by Kyocera Document Solutions Inc.). The image forming method will be described in detail in the second embodiment.

  The content of the color gamut adjusting agent is preferably 10.0% by mass or more and 40.0% by mass or less, and preferably 10.0% by mass or more and 30.0% by mass or less with respect to the mass of the black colorant. It is more preferable. When the content of the color gamut adjusting agent is within such a range, the color developability of the formed image tends to be improved.

  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 further contain another colorant as a colorant in addition to the black colorant and the color gamut adjusting agent. Another colorant can be appropriately selected from known colorants.

  The total content of the black colorant and the color gamut adjusting agent is preferably 70% by mass or more, more preferably 80% or more, and 90% or more with respect to the mass of the colorant. Further preferred is 100%.

<1-3. Release agent>
The toner core may contain a release agent as required. The release agent is usually used for the purpose of improving the toner fixing property and offset resistance.

  As the release agent, wax is preferable. Examples of the wax include ester wax, polyethylene wax, polypropylene wax, fluororesin wax, Fischer-Tropsch wax, paraffin wax, and montan wax. Of these, ester wax is more preferable. Examples of the ester wax include natural ester wax (specifically, synthetic ester wax, carnauba wax, or rice wax), and synthetic ester wax. These release agents can be used in combination of two or more.

  Of the ester waxes, synthetic ester waxes are preferred. By appropriately selecting a synthetic raw material, it is easy to adjust the melting point (temperature of the maximum endothermic peak in the DSC curve, Mpr) of the release agent measured using a differential scanning calorimeter to a suitable range described later. is there.

  The method for producing the synthetic ester wax is not particularly limited as long as it is a chemical synthesis method. For example, a synthetic ester wax can be synthesized by reacting an alcohol and a carboxylic acid in the presence of an acid catalyst. As another example, a synthetic ester wax can be synthesized using a known method in which a carboxylic acid halide and an alcohol are reacted. In addition, the raw material derived from a natural product may be sufficient as the raw material of synthetic ester wax, for example like the long chain fatty acid manufactured from natural fats and oils. Moreover, as synthetic ester wax, you may use the ester wax marketed as a synthetic product.

  The melting point of the release agent (the temperature of the maximum endothermic peak in the DSC curve, Mpr) is preferably 50 ° C. or higher and 100 ° C. or lower. The melting point (Mpr) of the release agent can be measured using a differential scanning calorimeter, for example, in the same manner as the measurement of the melting point (Mpc) of the crystalline resin. When the melting point (Mpr) of the release agent is within such a range, the toner including toner particles having a toner core containing such a release agent is excellent in low-temperature fixability and is used when fixing the toner at a high temperature. Even if it exists, it exists in the tendency for generation | occurrence | production of offset to be suppressed.

  The amount of the release agent used is preferably 1 part by mass or more and 30 parts by mass or less, and more preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

<1-4. Charge Control Agent>
The toner core may contain a charge control agent as necessary. The charge control agent is used for the purpose of improving the charge level of the toner and the charge rising property of the toner, and for obtaining a toner having excellent durability and stability. 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. When a component having a charging function is included in the shell layer, a charge control agent may not be used in the toner core. When developing with the toner positively charged, a positively chargeable charge control agent can be used. On the other hand, when developing with negatively charged toner, a negatively chargeable charge control agent can be used.

  The charge control agent can be appropriately selected from known charge control agents. Specific examples of the positively chargeable charge control agent include azine compounds (for example, pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2 , 4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5 -Thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4, 5-oxatriazine, phthalazine, quinazoline, and quinoxaline); direct dyes containing azine compounds (eg, azine fast red FC, azine fast) Red 12BK, azine violet BO, azine brown 3G, azine light brown GR, azine dark green BH / C, azine deep black EW, and azine deep black 3RL); nigrosine compounds (eg, nigrosine, nigrosine salt, and nigrosine) Derivatives); acid dyes containing nigrosine compounds (eg, nigrosine BK, nigrosine NB, and nigrosine Z); metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; and quaternary ammonium salts (eg, benzyldecylhexyl). Methylammonium and decyltrimethylammonium chloride). Among these positively chargeable charge control agents, a nigrosine compound is particularly preferable because it is easy to obtain suitable charge rising characteristics of the toner. These positively chargeable charge control agents may be used alone or in combination of two or more.

  A resin having a quaternary ammonium salt, carboxylate, or carboxyl group as a functional group can also be used as a positively chargeable charge control agent. More specifically, a styrene resin having a quaternary ammonium salt, an acrylic resin having a quaternary ammonium salt, a styrene-acrylic resin having a quaternary ammonium salt, a polyester resin having a quaternary ammonium salt, and a carboxylate A styrene resin having a carboxylate, an acrylic resin having a carboxylate, a styrene-acrylic resin having a carboxylate, a polyester resin having a carboxylate, a styrene resin having a carboxyl group, an acrylic resin having a carboxyl group, Examples thereof include styrene acrylic resins having a carboxyl group, and polyester resins having a carboxyl group. These resins may be oligomers or polymers.

  Specific examples of the negatively chargeable charge control agent include organometallic complexes and chelate compounds. Examples of the organometallic complex and the chelate compound include acetylacetone metal complexes (for example, aluminum acetylacetonate and iron (II) acetylacetonate), and salicylic acid-based metal complexes or salicylic acid-based metal salts (for example, 3,5-di- tert-butyl salicylate chromium) is preferable, and a salicylic acid metal complex or a salicylic acid metal salt is more preferable. These negatively chargeable charge control agents may be used singly or in combination of two or more.

  The use amount of the positively or negatively chargeable charge control agent is preferably 0.5 parts by mass or more and 20.0 parts by mass or less, and 1.0 part by mass when the total amount of the toner is 100 parts by mass. More preferably, it is 15.0 parts by mass or less.

<1-5. Magnetic content>
The toner core may contain magnetic powder in the binder resin as necessary. Toner manufactured using a toner core containing magnetic powder is used as a magnetic one-component developer. Suitable magnetic powders include iron such as ferrite or magnetite; ferromagnetic metals such as cobalt or nickel; alloys containing iron and / or ferromagnetic metals; compounds containing iron and / or ferromagnetic metals A ferromagnetic alloy subjected to a ferromagnetization treatment such as heat treatment; chromium dioxide.

  The particle size of the magnetic powder is preferably 0.1 μm or more and 1.0 μm or less. When magnetic powder having a particle diameter in such a range is used, it is easy to uniformly disperse the magnetic powder in the binder resin.

  The amount of magnetic powder used is preferably 35 parts by weight or more and 60 parts by weight or less, and 40 parts by weight or more and 60 parts by weight or less with respect to 100 parts by weight of the total amount of toner when toner is used as a one-component developer. It is more preferable that

<2. Shell layer>
The toner particles contained in the toner of the present embodiment include a shell layer. The shell layer is provided to cover the toner core. The shell layer includes a thermosetting resin and a thermoplastic resin.

  When the shell layer contains a thermosetting resin and a thermoplastic resin, the heat resistant storage stability of the toner tends to be improved. When the shell layer contains only the thermoplastic resin, the toner particles contained in the toner are easily fused to each other when the toner is stored at a high temperature. On the other hand, when the shell layer contains only a thermosetting resin, when the toner is heated at the time of fixing, the toner particles contained in the toner are not easily destroyed and the low-temperature fixability of the toner tends to be inferior.

  The shell layer is formed by mixing or reacting a thermosetting resin material (for example, a thermosetting resin monomer or prepolymer) and a thermoplastic resin material (for example, a thermoplastic resin). The In the shell layer, the thermosetting resin and the thermoplastic resin are mixed and solidified, and the region formed of the thermosetting resin and the region formed of the thermoplastic resin are mixed in the shell layer. May be. The shell layer may contain a thermosetting resin raw material (for example, a thermosetting resin monomer or prepolymer that is not polymerized or polycondensed). Further, in the shell layer, at least a part of the substituents that the thermosetting resin has and at least a part of the substituents that the thermoplastic resin has may be chemically bonded (crosslinked).

  When the substituent of the thermosetting resin and the substituent of the thermoplastic resin are chemically bonded (crosslinked) in the shell layer, the shell layer has an appropriate flexibility due to the thermoplastic resin. . Furthermore, the shell layer also has an appropriate mechanical strength due to the three-dimensional cross-linking structure formed by the thermosetting resin as well as an appropriate flexibility. Toner particles having such a shell layer tend not to be easily destroyed during storage and transportation. On the other hand, such toner particles tend to be easily destroyed when temperature and pressure are applied during fixing. As a result, the toner of this embodiment tends to be excellent in heat-resistant storage stability and low-temperature fixability even when the shell layer is a thin film.

  Hereinafter, the thermosetting resin and thermoplastic resin contained in the shell layer will be described.

  <2-1. Thermosetting resin>

  The thermosetting resin contained in the shell layer is one or more resins selected from the amino resin group consisting of melamine resin, urea resin, and glyoxal resin. Examples of the raw material of the thermosetting resin contained in the shell layer include a monomer of melamine resin, a monomer of urea resin, and a monomer of glyoxal resin.

  Melamine resin is a polycondensate of melamine and formaldehyde. The monomer used to form the melamine resin is melamine. Urea resin is a polycondensate of urea and formaldehyde. The monomer used to form the urea resin is urea. Glyoxal resin is a polycondensate of a reaction product of glyoxal and urea with formaldehyde. The monomer used to form the glioxal resin is the reaction product of glyoxal and urea.

  Urea to be reacted with melamine, urea, and glyoxal may be subjected to known modification. For example, a monomer of a thermosetting resin can be used as a derivative methylolated with formaldehyde before reacting with a thermoplastic resin.

  Melamine, urea, and the reaction product of glyoxal and urea may be used in the form of a prepolymer (hereinafter sometimes referred to as an initial polymer). Here, the prepolymer means an intermediate product obtained by stopping the polymerization reaction or polycondensation reaction of monomers at a stage before the polymerization degree reaches the polymerization degree of the polymer.

  The shell layer is derived from the reaction product of nitrogen atoms derived from melamine, which is a monomer of melamine resin, nitrogen atoms derived from urea, which is a monomer of urea resin, and / or glyoxal, which is a monomer of glyoxal resin. Containing nitrogen atoms. A toner having a shell layer containing nitrogen atoms is easily positively charged. Therefore, when an image is formed by positively charging the toner of this embodiment, it is easy to positively charge the toner particles contained in the toner to a desired charge amount. The content of nitrogen atoms in the shell layer is preferably 10% by mass or more from the viewpoint that the toner particles contained in the toner are easily positively charged to a desired charge amount.

<2-2. Thermoplastic resin>
The thermoplastic resin includes a functional group that is reactive with a functional group (for example, a methylol group and an amino group) that a thermosetting resin raw material (for example, a monomer and / or a prepolymer of the thermosetting resin) has. It is preferable. The functional group having reactivity with the functional group (for example, methylol group and amino group) possessed by the raw material of the thermosetting resin includes a functional group containing an active hydrogen atom (for example, a hydroxyl group, a carboxyl group, and an amino group). Can be mentioned. The amino group may be contained in the thermoplastic resin as a carbamoyl group (—CONH ₂ ). Since the formation of the shell layer is easy, the thermoplastic resin is derived from a resin containing a unit derived from (meth) acrylamide, or a monomer having a functional group such as a carbodiimide group, an oxazoline group, or a glycidyl group. Resins containing units are preferred.

  Specific examples of the thermoplastic resin used for forming the shell layer include (meth) acrylic resin, styrene- (meth) acrylic copolymer, silicone- (meth) acrylic graft copolymer, urethane resin, polyester. Resin, polyvinyl alcohol, and ethylene vinyl alcohol copolymer are mentioned. These resins may contain a unit derived from a monomer having a functional group such as a carbodiimide group, an oxazoline group, and a glycidyl group. Among these, (meth) acrylic resins, styrene- (meth) acrylic copolymers, or silicone- (meth) acrylic graft copolymers are preferable, and (meth) acrylic resins are more preferable. As the (meth) acrylic resin, a (meth) acrylamide resin is preferable.

  In some cases, acryl and methacryl are collectively referred to as “(meth) acryl”.

  Examples of (meth) acrylic monomers that can be used to prepare (meth) acrylic resins include (meth) acrylic acid; (meth) acrylic acid alkyl esters (for example, methyl (meth) acrylate, (meth ) Ethyl acrylate, n-propyl (meth) acrylate, and n-butyl (meth) acrylate); (meth) acrylic acid aryl esters (eg, phenyl (meth) acrylate); hydroxyalkyl (meth) acrylate Esters (eg, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate); (meth) acrylamide Ethylene oxide adducts of (meth) acrylic acid; and (meth) acrylic acid s Alkyl ethers of ethylene oxide adducts of Le (e.g., methyl ether, ethyl ether, n- propyl ether, and n- butyl ether) and the like. Of these, (meth) acrylamide is preferable.

  The shell layer is preferably formed in an aqueous medium because the binder resin is not easily dissolved and the release agent contained in the toner core is hardly dissolved. For this reason, it is preferable that the thermoplastic resin used for forming the shell layer is water-soluble. In particular, it is preferable to use a thermoplastic resin as an aqueous solution for forming the shell layer.

  In the shell layer, the ratio (Ws / Wp) of the mass (Ws) of the thermosetting resin to the mass (Wp) of the thermoplastic resin is preferably 1/40 or more and 1/2 or less, and 1/8 or more and 3 It is more preferable that it is / 8 or less.

  The total content of the thermosetting resin and the thermoplastic resin in the shell layer is preferably 70% by mass or more, more preferably 80% by mass or more, and 90% by mass with respect to the mass of the shell layer. % Or more is more preferable, and 100% by mass is particularly preferable.

  The thickness of the shell layer is 5 nm or more and 50 nm or less. The thickness of the shell layer is more preferably 5 nm or more and 20 nm or less. When an image is formed using toner containing toner particles having a shell layer that is too thick, the shell layer is not easily destroyed even when pressure is applied to the toner particles when fixing the toner to the recording medium. Therefore, the softening or melting of the binder resin contained in the toner core and the softening or melting of the release agent do not proceed quickly, and it is difficult to fix the toner on the recording medium in a low temperature range. On the other hand, a shell layer that is too thin tends to have low strength. When the strength of the shell layer is low, the shell layer is easily broken by an impact applied to the toner during transportation. Further, when the toner is stored at a high temperature, the toner particles in which at least a part of the shell layer is broken easily aggregate. This is because, under high temperature conditions, a component such as a release agent tends to ooze out to the surface of the toner particles through the location where the shell layer is broken.

  The thickness of the shell layer can be measured by analyzing a TEM image of a cross section of the toner particles using commercially available image analysis software (for example, “WinROOF” manufactured by Mitani Corporation). Specifically, two straight lines that are orthogonal to each other at substantially the center point of the cross section of the toner particle are drawn, and the lengths of four points that intersect the shell layer on the two straight lines are measured. The average value of the four lengths thus measured is taken as the thickness of the shell layer of one toner particle to be measured. Such a measurement of the thickness of the shell layer is performed on ten toner particles, and an average value of the thicknesses of the shell layers included in each of the ten toner particles to be measured is obtained. The obtained average value is taken as the thickness of the shell layer provided in the toner.

  When the shell layer is too thin (for example, when the shell layer is less than 5 nm), it is difficult to measure the thickness of the shell layer because the interface between the shell layer and the toner core is unclear on the TEM image. There is. In such a case, a combination of TEM imaging and electron energy loss spectroscopy (EELS) is used to perform mapping of elements (for example, nitrogen) characteristic of the shell layer in the TEM image, and the shell layer and the toner core The thickness of the shell layer may be measured by clarifying the interface.

The thickness of the shell layer is changed as appropriate according to the amount of shell layer raw material (for example, a thermosetting resin monomer, a thermosetting resin prepolymer, or a thermoplastic resin) used to form the shell layer. It can be adjusted by doing. The thickness of the shell layer can also be obtained from the following formula using the amount of the thermosetting resin and the amount of the thermoplastic resin with respect to the specific surface area of the toner core.
Shell layer thickness = (amount of thermosetting resin + amount of thermoplastic resin) / specific surface area of toner core

<3. External additive>
An external additive may be attached to the surface of the toner core covered with the shell layer, if necessary.

  Examples of the external additive include silica and metal oxide. Examples of the metal oxide include alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate.

  The particle diameter of the external additive is preferably 0.01 μm or more and 1.0 μm or less.

  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.

<4. Career>
The toner may be mixed with a desired carrier and used as a two-component developer. When preparing a two-component developer, it is preferable to use a magnetic carrier.

  Suitable carriers include carriers in which the carrier core is coated with a resin. Specific examples of carrier cores include iron, oxidized iron, reduced iron, magnetite, copper, silicon steel, ferrite, nickel, or cobalt particles; alloys of these materials with metals such as manganese, zinc, and aluminum Particles of iron-nickel alloy; particles of iron-cobalt alloy; particles of ceramics; and particles of high dielectric constant materials. As the carrier, a resin carrier in which the above magnetic particles are dispersed in a resin can also be used. Examples of ceramics used as ceramic particles include titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide, zirconium oxide, silicon carbide, magnesium titanate, barium titanate, lithium titanate, lead titanate, Examples include lead zirconate and lithium niobate. Examples of the high dielectric constant material used as the particles of the high dielectric constant material include ammonium dihydrogen phosphate, potassium dihydrogen phosphate, and Rochelle salt.

  Examples of the resin covering the carrier core include (meth) acrylic polymers, styrene polymers, styrene- (meth) acrylic copolymers, olefin polymers (for example, polyethylene, chlorinated polyethylene, and polypropylene). ), Polyvinyl chloride, polyvinyl acetate, polycarbonate, cellulose resin, polyester resin, unsaturated polyester resin, polyamide resin, urethane resin, epoxy resin, silicone resin, fluororesin (eg, polytetrafluoroethylene, polychlorotrifluoroethylene) And polyvinylidene fluoride), phenol resin, xylene resin, diallyl phthalate resin, polyacetal resin, and amino resin. One of these resins may be used alone, or two or more thereof may be used in combination.

  The particle diameter of the carrier is preferably 20 μm or more and 120 μm or less, and more preferably 25 μm or more and 80 μm or less. The particle diameter of the carrier can be measured by, for example, an electron microscope.

  When the toner is used as a two-component developer, the toner content is preferably 3% by mass or more and 20% by mass or less, and preferably 5% by mass or more and 15% by mass or less with respect to the mass of the two-component developer. It is preferable.

  The glass transition point (Tgt) of the toner is preferably 30 ° C. or higher and 50 ° C. or lower. The softening point (Tmt) of the toner is preferably 70 ° C. or higher and 100 ° C. or lower. When the glass transition point (Tgt) and softening point (Tmt) of the toner are within such ranges, the heat-resistant storage stability and low-temperature fixability of the toner can be improved, and offset when fixing the toner at a high temperature. It tends to be possible to suppress the occurrence of.

  The glass transition point (Tgt) and softening point (Tmt) of the toner are the same as the glass transition point (Tga) of the non-crystalline resin and the softening point (Tma) of the non-crystalline resin, using the toner as a sample. It can be measured by the method. In the measurement of the glass transition point (Tgt) of the toner, when the glass transition point is observed in multiple stages, the point observed at the lowest temperature is defined as the glass transition point (Tgt) of the toner. The glass transition point (Tgt) and softening point (Tmt) of the toner can be adjusted by adjusting the type and composition of the binder resin in the toner core and the type and composition of the release agent.

<5. Toner Production Method>
The method for producing the toner is not particularly limited as long as the toner core can be coated with the shell layer. Hereinafter, a toner core manufacturing method and a shell layer forming method will be described with respect to a preferable toner manufacturing method.

<5-1. Manufacturing method of toner core>
The method for producing the toner core is not particularly limited as long as the colorant and optional components (for example, charge control agent, release agent, and / or magnetic powder) can be well dispersed in the binder resin. The method for producing the toner core can be appropriately selected from known methods. Examples of the manufacturing method of the toner core include the following pulverization method and aggregation method.

(Crushing method)
In the pulverization method, first, a binder resin, a colorant, and optional components (for example, a charge control agent, a release agent, and / or magnetic powder) are mixed. The resulting mixture is melted and kneaded. The resulting melt-kneaded product is pulverized and classified to obtain a toner core having a desired particle size. The pulverization method has an advantage that the toner core can be easily prepared as compared with the aggregation method described later. On the other hand, the pulverization method is disadvantageous than the aggregation method in that a toner core having a high average circularity is difficult to obtain because a toner core is obtained through a pulverization step. However, in the shell layer forming step described later, the shell layer curing reaction proceeds by heating the shell layer raw material. At this time, the slightly softened toner core contracts due to surface tension, so that the toner core tends to be spherical. Therefore, when the toner core is manufactured by a pulverization method, it is considered that no major disadvantage is caused even if the average circularity of the toner core is somewhat low. Therefore, a pulverization method is preferable as a manufacturing method of the toner core.

(Aggregation method)
In the aggregation method, first, fine particles containing a binder resin, a colorant, and optional components (for example, a charge control agent, a release agent, and / or magnetic powder) are aggregated in an aqueous medium to obtain aggregated particles. The obtained aggregated particles are heated to unitize the components contained in the aggregated particles. By coalescence, an aqueous dispersion containing a toner core is obtained. The dispersant and the like are removed from the obtained aqueous dispersion, and the toner core is washed. As a result, a toner core is obtained.

  In the production of the toner core, the zeta potential of the toner core measured in an aqueous medium adjusted to pH 4 is preferably negative (less than 0 mV), more preferably −10 mV or less. The zeta potential of the toner core in an aqueous medium adjusted to pH 4 can be measured, for example, by the following method.

(Method for measuring zeta potential of toner core in aqueous medium at pH 4)
Using a magnetic stirrer, 0.2 g of toner core, 80 mL of ion-exchanged water, and 20 g of nonionic surfactant (for example, “polyvinylpyrrolidone K-85” manufactured by Nippon Shokubai Co., Ltd., water concentration 5 mass%, solid content concentration 95%) And mix. Thus, the toner core is uniformly dispersed in a solvent (for example, ion exchange water) to obtain a dispersion. Dilute hydrochloric acid is added to the obtained dispersion to adjust the pH of the dispersion to 4. As a result, a dispersion of a toner core having a pH of 4 is obtained. Using the toner core dispersion at pH 4 as a sample, the zeta potential of the toner core in the dispersion is measured. The zeta potential is measured using a zeta potential / particle size distribution measuring apparatus (for example, “Delsa Nano HC” manufactured by Beckman Coulter, Inc.).

  When a standard carrier and a toner core of 7% by mass with respect to the mass of the standard carrier are mixed for 30 minutes using a mixing device (for example, “Tabra (registered trademark) mixer” manufactured by WAB), the triboelectric charge amount of the toner core is The negative polarity (less than 0 μC / g) is preferable, and the negative polarity is more preferably −10 μC / g or less. The triboelectric charge amount can be measured, for example, by the following method.

(Measurement method of triboelectric charge)
A standard carrier N-01 (standard carrier for negatively charged polar toner) provided by the Imaging Society of Japan and a toner core of 7% by mass with respect to the mass of the standard carrier are mixed with a mixing device (for example, “Tabra (registered by WAB)” Trademark) mixer)) for 30 minutes. Using the obtained mixture as a sample, the triboelectric charge amount of the toner core is measured using a Q / m meter (for example, “MODEL 210HS-2A” manufactured by Trek). The amount of triboelectricity measured in this way is an indicator of whether the toner core is easily charged to a positive or negative polarity, and the ease with which the toner core is charged.

  Usually, in order to form a uniform shell layer on the toner core, the toner core is often highly dispersed in an aqueous medium containing a dispersant. However, when the triboelectric charge amount of the toner core with the standard carrier is negative (less than 0 μC / g), the shell core material (for example, a nitrogen-containing compound and positive in the aqueous medium) is added to the toner core in the aqueous medium. The monomer and / or prepolymer of the thermosetting resin that is electrically charged) is electrically attracted. On the surface of the toner core, the reaction between the thermoplastic resin material adsorbed on the toner core (for example, a monomer and / or prepolymer of the thermosetting resin) and the thermoplastic resin proceeds favorably. For this reason, when a shell layer is formed on the surface of the toner core using a toner core that is negatively charged in an aqueous medium, a uniform shell layer is formed on the surface of the toner core even when the toner core is not highly dispersed in the aqueous medium using a dispersant. Tend to form.

  Even when the zeta potential of the toner core in an aqueous medium at pH 4 is negative (less than 0 mV), the same effect tends to be obtained when a shell layer is formed on the surface of the toner core in the aqueous medium.

  When toner particles are produced using a toner core in which at least one of a triboelectric charge amount with a standard carrier and a zeta potential in an aqueous medium of pH 4 has a negative polarity, the toner core is uniform even when no dispersant is used. It tends to be easy to obtain toner particles coated with a shell layer. Therefore, the total organic carbon concentration of the wastewater discharged when producing toner particles is reduced to a low level (for example, 15 mg / L or less) without using a dispersant having a very high wastewater load and without diluting the wastewater. It becomes possible.

<5-2. Shell layer forming method>
By coating the obtained toner core with a shell layer, toner mother particles can be obtained. Hereinafter, the shell layer forming method will be described.

  As a raw material for forming the shell layer, at least one of melamine, urea, a reaction product of glyoxal and urea, and a precursor (methylolated product) generated by addition reaction of these with formaldehyde is used. . A thermoplastic resin is further used as a raw material for forming the shell layer.

  When forming the shell layer, it is preferable to prevent dissolution of the binder resin and elution of components such as a release agent contained in the toner core in the solvent used for forming the shell layer. For this reason, formation of a shell layer can be suitably performed in a solvent such as water.

  The shell layer is preferably formed by adding a toner core to an aqueous solution of the raw material for forming the shell layer (an aqueous medium containing the raw material). Examples of a method for satisfactorily dispersing the toner core in the aqueous medium after adding the toner core in the aqueous medium include a method in which the toner core is mechanically dispersed in the aqueous medium using an apparatus capable of strongly stirring the dispersion. It is done.

  As an apparatus that can vigorously stir the dispersion, for example, a mixing apparatus (for example, “Hibismix” manufactured by Primics Co., Ltd.) can be used.

  It is preferable to adjust the pH of the aqueous solution to about 4 using an acidic substance before adding the toner core to the raw material aqueous solution for forming the shell layer. By adjusting the pH of the aqueous solution to the acidic side, the polycondensation reaction of the raw materials for forming the shell layer tends to be promoted.

  If necessary, after adjusting the pH of the aqueous solution of the raw material for forming the shell layer (the aqueous medium containing the raw material), the raw material for forming the shell layer and the toner core are mixed in the aqueous medium. Thereafter, the reaction between the surface of the toner core and the raw material for forming the shell layer is allowed to proceed in the aqueous dispersion.

  The temperature at which the shell layer is formed is preferably 40 ° C. or higher and 95 ° C. or lower, and more preferably 50 ° C. or higher and 80 ° C. or lower. When the shell layer is formed at such a temperature, the formation of the shell layer tends to proceed well.

  As a result, a shell layer covering the toner core is formed, and an aqueous dispersion containing toner mother particles is obtained. The aqueous dispersion containing the toner base particles is cooled to room temperature. Thereafter, one or more steps selected from a toner mother particle cleaning step, a drying step, and an external addition step are performed as necessary. As a result, a toner is obtained. Hereinafter, the cleaning process, the drying process, and the external addition process will be described.

<5-3. Cleaning process>
The toner base particles are washed with water as necessary. Examples of the cleaning method include a method in which toner base particles are collected as a wet cake by solid-liquid separation from an aqueous dispersion containing toner base particles, and the resulting wet cake is washed with water. As another cleaning method, there is a method in which the toner base particles in the dispersion of the toner base particles are settled, the supernatant liquid is replaced with water, and the toner base particles are redispersed in water after the replacement.

<5-4. Drying process>
The toner base particles may be dried as necessary. Examples of the method for drying the toner base particles include a method using a dryer such as a spray dryer, a fluidized bed dryer, a vacuum freeze dryer, and a vacuum dryer. Among these methods, a method using a spray dryer is more preferable because aggregation of toner mother particles during drying is easily suppressed. In the case of using a spray dryer, the external additive can be adhered to the surface of the toner base particles simultaneously with drying by spraying a dispersion of the external additive such as silica together with the dispersion of the toner base particles.

<5-5. External process>
An external additive may be attached to the surface of the toner base particles as necessary. As a method of attaching an external additive to the surface of the obtained toner base particles, the conditions are adjusted so that the external additive is not buried in the surface of the toner base particles, and an FM mixer or a Nauter mixer (registered trademark) is used. A method of mixing the toner base particles and the external additive using such a mixer can be mentioned.

  The toner of this embodiment has been described above. The toner according to the exemplary embodiment is excellent in color developability, heat resistant storage stability, charging stability, and image density stability. For this reason, the toner of this embodiment can be suitably used in various image forming apparatuses.

<Second Embodiment: Image Forming Method>
The second embodiment relates to an image forming method. The image forming method of this embodiment is a method of forming an image using the toner of the first embodiment. The image forming method includes a transfer process and a fixing process.

  Hereinafter, the image forming method of the present embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus 6 used in the image forming method of the present embodiment.

  The image forming apparatus 6 includes an image carrier (corresponding to a photoconductor) 1, a charging unit (corresponding to a charging device) 27, an exposure unit (corresponding to an exposure device) 28, a developing unit 29, and a transfer unit. . The charging unit 27 charges the surface of the image carrier 1. The exposure unit 28 exposes the charged surface of the image carrier 1 to form an electrostatic latent image on the surface of the image carrier 1. The developing unit 29 develops the electrostatic latent image as a toner image. The transfer unit transfers the toner image from the image carrier 1 to a transfer target (corresponding to an intermediate transfer belt) 20.

  The image forming apparatus 6 is not particularly limited as long as it is an electrophotographic image forming apparatus. The image forming apparatus 6 may be, for example, a monochrome image forming apparatus or a color image forming apparatus. In order to form toner images of different colors using different color toners, the image forming apparatus 6 of the present embodiment may be a tandem color image forming apparatus.

  Hereinafter, the image forming apparatus 6 will be described by taking a tandem color image forming apparatus as an example. The image forming apparatus 6 includes a plurality of photoreceptors 1 arranged in parallel in a predetermined direction and a plurality of developing units 29. Each of the plurality of developing units 29 is disposed to face the photoreceptor 1. The plurality of developing units 29 carry and carry toner on the surface of the developing unit 29. Each of the plurality of developing units 29 includes a developing roller. The developing roller supplies the conveyed toner to the surface of the corresponding photoreceptor 1. The toner used is the toner of the first embodiment.

  As shown in FIG. 1, the image forming apparatus 6 has a box-shaped device housing 7. In the device housing 7, a paper feeding unit 8, an image forming unit 9, and a fixing unit 10 are provided. The paper feed unit 8 feeds the paper P. The image forming unit 9 transfers the toner image based on the image data to the paper P while conveying the paper P fed from the paper feeding unit 8. The fixing unit 10 fixes the unfixed toner image transferred on the paper P by the image forming unit 9 to the paper P. Further, a paper discharge unit 11 is provided on the upper surface of the device housing 7. The paper discharge unit 11 discharges the paper P fixed by the fixing unit 10.

  The paper supply unit 8 includes a paper supply cassette 12, a first pickup roller 13, paper supply rollers 14, 15 and 16, and a registration roller pair 17. The paper feed cassette 12 is provided so as to be detachable from the device housing 7. Various sizes of paper P are stored in the paper feed cassette 12. The first pickup roller 13 is provided at the upper left position of the paper feed cassette 12. The first pickup roller 13 takes out the sheets P stored in the sheet feeding cassette 12 one by one. The paper feed rollers 14, 15 and 16 convey the paper P taken out by the first pickup roller 13. The registration roller pair 17 temporarily supplies the paper P conveyed by the paper feed rollers 14, 15, and 16 to the image forming unit 9 at a predetermined timing.

  The paper feed unit 8 further includes a manual feed tray (not shown) and a second pickup roller 18. The manual feed tray is attached to the left side surface of the device housing 7. The second pickup roller 18 takes out the paper P placed on the manual feed tray. The paper P taken out by the second pickup roller 18 is conveyed by the paper feed rollers 14, 15 and 16, and is supplied to the image forming unit 9 by the registration roller pair 17 at a predetermined timing.

  The image forming unit 9 includes an image forming unit 19, an intermediate transfer belt 20, and a secondary transfer roller 21. A toner image is primarily transferred onto the intermediate transfer belt 20 by the image forming unit 19 on the surface of the intermediate transfer belt 20 (contact surface with the primary transfer roller 33). The toner image to be primarily transferred is formed based on image data transmitted from a host device such as a computer. The secondary transfer roller 21 secondarily transfers the toner image on the intermediate transfer belt 20 onto the paper P fed from the paper feed cassette 12.

  The image forming unit 19 includes a yellow toner supply unit 25, a magenta toner supply unit 24, and a cyan toner from the upstream side (right side in FIG. 1) to the downstream side of the driven roller 31 in the rotation direction of the intermediate transfer belt 20. A supply unit 23 and a black toner supply unit 22 are sequentially arranged. In the units 22, 23, 24, and 25, the photoreceptor 1 is disposed at the center position of each unit. The photoreceptor 1 is disposed so as to be rotatable in the direction of an arrow (clockwise).

  Around each photoconductor 1, a charging unit 27, an exposure unit 28, and a developing unit 29 are upstream of the contact portion between each photoconductor 1 and the intermediate transfer belt 20 in the rotation direction of each photoconductor 1. They are arranged in order. Further, a cleaning device (not shown) is disposed downstream of the contact portion between each photoconductor 1 and the intermediate transfer belt 20 in the rotation direction of each photoconductor 1.

The charging unit 27 charges the surface of the photoreceptor 1. Specifically, the charging unit 27 uniformly charges the peripheral surface of the photoreceptor 1 rotated in the direction of the arrow. The charging unit 27 is not particularly limited as long as the peripheral surface of the photoreceptor 1 can be uniformly charged. The charging unit 27 may be a non-contact charging device or a contact charging device. Examples of the charging unit 27 include a corona charging device, a charging roller, and a charging brush. The charging unit 27 is preferably a contact-type charging device (specifically, a charging roller or a charging brush), and more preferably a charging roller. By using the charging portion 27 of the contact type, gas generated from the charging unit 27 (e.g., gas of nitrogen oxides, such as gas, or NO _X oxidising substances such as ozone) easily reduce emissions of Become. As a result, the deterioration of the photosensitive layer due to gas is suppressed, and it is considered that the design considering the office environment can be achieved.

  When the charging unit 27 includes a contact-type charging roller, the charging roller charges the peripheral surface (surface) of the photoconductor 1 while being in contact with the photoconductor 1. As such a charging roller, for example, a charging roller that rotates depending on the rotation of the photosensitive member 1 while being in contact with the photosensitive member 1 can be used. Moreover, as a charging roller, the charging roller by which the surface part was comprised with resin at least is mentioned, for example. A specific charging roller includes, for example, a core metal rotatably supported, a resin layer formed on the core metal, and a voltage application unit that applies a voltage to the core metal. The charging unit 27 including such a charging roller can charge the surface of the photoreceptor 1 that is in contact with the resin through the resin layer when the voltage application unit applies a voltage to the cored bar.

  The voltage applied by the charging unit 27 is not particularly limited. However, since a suitable image is formed, the charging unit 27 is more than the case where the charging unit 27 applies an AC voltage or the charging unit 27 applies a superimposed voltage obtained by superimposing the AC voltage on the DC voltage. However, it is preferable to apply only a DC voltage.

  The resin constituting the resin layer of the charging roller is not particularly limited as long as the peripheral surface of the photoreceptor 1 can be charged satisfactorily. Specific examples of the resin constituting the resin layer include a silicone resin, a urethane resin, and a silicone-modified resin. The resin layer may contain an inorganic filler.

  A static eliminator (not shown) may be provided on the upstream side of the charging unit 27 in the rotation direction of the photoreceptor 1. The static eliminator neutralizes the peripheral surface of the photoreceptor 1 after the primary transfer of the toner image to the intermediate transfer belt 20 is completed. The peripheral surface of the photoreceptor 1 cleaned and discharged by the cleaning device and the charge eliminator is sent to the charging unit 27 and newly charged.

  The exposure unit 28 is a so-called laser scanning unit. The exposure unit 28 exposes the charged surface of the photoconductor 1 to form an electrostatic latent image on the surface of the photoconductor 1. Specifically, the exposure unit 28 irradiates the peripheral surface (surface) of the photoreceptor 1 uniformly charged by the charging unit 27 with laser light based on image data input from a host device such as a personal computer. . Thereby, an electrostatic latent image based on the image data is formed on the peripheral surface (front surface) of the photoreceptor 1.

  The developing unit 29 develops the electrostatic latent image as a toner image. Specifically, the developing unit 29 supplies toner to the peripheral surface of the photoreceptor 1 on which the electrostatic latent image is formed, and forms a toner image based on the image data. Then, the formed toner image is primarily transferred to the intermediate transfer belt 20. The cleaning device cleans the toner remaining on the peripheral surface of the photoreceptor 1 after the primary transfer of the toner image to the intermediate transfer belt 20 is completed.

  The intermediate transfer belt 20 is an endless belt rotating body. The intermediate transfer belt 20 is stretched around a driving roller 30, a driven roller 31, a backup roller 32, and a plurality of primary transfer rollers 33. The intermediate transfer belt 20 is disposed so that the peripheral surfaces of the plurality of photosensitive members 1 are in contact with the surface (contact surface) of the intermediate transfer belt 20.

  Further, the intermediate transfer belt 20 is pressed against the photoconductor 1 by a primary transfer roller 33 disposed to face each photoconductor 1. In the pressed state, the intermediate transfer belt 20 rotates endlessly in the direction of the arrow (counterclockwise) by the plurality of primary transfer rollers 33. The driving roller 30 is rotationally driven by a driving source such as a stepping motor, and gives a driving force for rotating the intermediate transfer belt 20 endlessly. The driven roller 31, the backup roller 32, and the plurality of primary transfer rollers 33 are rotatably provided. The driven roller 31, the backup roller 32, and the primary transfer roller 33 rotate following the endless rotation of the intermediate transfer belt 20 by the driving roller 30. The driven roller 31, the backup roller 32, and the primary transfer roller 33 are driven to rotate via the intermediate transfer belt 20 according to the main rotation of the driving roller 30 and support the intermediate transfer belt 20.

  The transfer unit transfers the toner image from the image carrier 1 to the intermediate transfer belt 20. Specifically, the primary transfer roller 33 applies a primary transfer bias (specifically, a bias having a polarity opposite to the charging polarity of the toner) to the intermediate transfer belt 20. As a result, the toner image formed on each photoconductor 1 is sequentially transferred (primary transfer) to the intermediate transfer belt 20 between each photoconductor 1 and the primary transfer roller 33.

  The secondary transfer roller 21 applies a secondary transfer bias (specifically, a bias having a polarity opposite to that of the toner image) to a recording medium (for example, paper P). As a result, the toner image primarily transferred onto the intermediate transfer belt 20 is transferred onto the paper P between the secondary transfer roller 21 and the backup roller 32. As a result, an unfixed toner image is transferred onto the paper P.

Here, the image forming method of the present embodiment includes a transfer step. In the transfer process, a transfer bias is applied to the recording medium. This corresponds to the operation of applying the secondary transfer bias to the paper P by the secondary transfer roller 21 described above. In the transfer step, it is preferable to apply a secondary transfer bias to the paper P so that the amount of toner loaded on the paper P is 0.4 mg / cm ² . The linear velocity at which the paper P is conveyed is preferably 200 mm / second or more and 220 mm / second or less.

  The fixing unit 10 fixes the unfixed toner image transferred to the paper P by the image forming unit 9. The fixing unit 10 includes a heating roller 34 and a pressure roller 35. The heating roller 34 is heated by an energized heating element. The pressure roller 35 is disposed to face the heating roller 34, and the circumferential surface of the pressure roller 35 is pressed against the circumferential surface of the heating roller 34.

  The transfer image transferred to the paper P by the secondary transfer roller 21 in the image forming unit 9 is fixed to the paper P by a fixing process by heating when the paper P passes between the heating roller 34 and the pressure roller 35. The Then, the paper P subjected to the fixing process is discharged to the paper discharge unit 11. In addition, a plurality of transport rollers 36 are disposed at appropriate positions between the fixing unit 10 and the paper discharge unit 11.

  Here, the image forming method of the present embodiment includes a fixing step. In the fixing step, the toner is fixed on the recording medium. This corresponds to the fixing operation on the paper P by the fixing unit 10 described above. In order to form an image having a desired color development property, the fixing temperature by the heating roller 34 is preferably 150 ° C. or higher and 170 ° C. or lower. The fixing pressure by the pressure roller 35 is preferably 210N or more and 230N or less. The distance (nip width) between the heating roller 34 and the pressure roller 35 is preferably 6.0 mm or more and 6.5 mm or less.

  The paper discharge unit 11 is formed by recessing the top of the device housing 7. A paper discharge tray 37 that receives the discharged paper P is provided at the bottom of the recessed portion.

The image formed on the paper P by the above-described method preferably has a desired color developability. Specifically, it is preferable that the a ^* value of the image is -4 or more and 1 or less, the b ^* value is -4 or more and 1 or less, and the L ^* value is 22 or less.

  The image forming method of this embodiment has been described above with reference to FIG. According to the image forming method of the present embodiment, an image having suitable color developability and image density can be formed by using the toner of the first embodiment. Furthermore, according to the image forming method of the present embodiment, it is possible to suppress the occurrence of fog in the formed image.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the scope of the examples.

  Each physical property in Examples and Comparative Examples was measured by the following methods.

(Glass transition point)
The glass transition point (Tga) of the amorphous polyester resin was determined from the change point of the specific heat of the amorphous polyester resin using a differential scanning calorimeter (DSC). More specifically, a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.) was used as a measuring device. The glass transition point (Tga) of the amorphous polyester resin was determined by measuring the endothermic curve of the amorphous polyester resin. 10 mg of a sample (non-crystalline polyester resin) was put in an aluminum pan, and an empty aluminum pan was used as a reference. An endothermic curve of the amorphous polyester resin was obtained by measurement under the conditions of a measurement temperature range of 25 ° C. or more and 200 ° C. or less and a temperature increase rate of 10 ° C./min. From the obtained endothermic polarity, the glass transition point (Tga) of the amorphous polyester resin was determined.

(Softening point)
The softening point (Tma) of the amorphous polyester resin was measured by using a Koka type flow tester (“CFT-500D” manufactured by Shimadzu Corporation). A sample (non-crystalline polyester resin) was set in a Koka type flow tester. A 1 cm ³ sample was melted and flowed out under conditions of a die pore diameter of 1 mm, a plunger load of 20 kg / cm ² , and a heating rate of 6 ° C./min. Thereby, the softening point (Tma) was measured. The softening point (Tma) of the amorphous resin was read from an S-shaped curve with respect to temperature (° C.) / Stroke (mm) obtained by measurement with a Koka flow tester. Specifically, the maximum value of the stroke and S _1, the stroke value of the low-temperature side of the base line was S _2. The temperature at which the stroke value in the S-curve was (S ₁ + S ₂ ) / 2 was taken as the softening point (Tma) of the sample.

(Melting point)
The melting point (Mpc) of the crystalline polyester resin was measured using a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.). A sample (crystalline polyester resin) of 10 mg to 15 mg was placed in an aluminum dish. Subsequently, an aluminum dish was set on the measurement part of the DSC. An empty aluminum dish was used as a reference. 30 ° C. was set as the measurement start temperature, and the temperature was raised to 170 ° C. at a rate of 10 ° C./min. The maximum peak temperature of the heat of fusion observed during the temperature rise was taken as the melting point (Mpc) of the crystalline polyester resin.

(Crystallinity index)
The crystallinity index of the crystalline resin and the resin used as the non-crystalline resin is a ratio (Tm) between the softening point (Tm) of the resin and the melting point of the resin (the temperature of the maximum endothermic peak in the DSC curve, Mp). / Mp). The softening point (Tm) and melting point (Mp) of the resin were measured in the same manner as the above-described measuring method of the softening point (Tma) and melting point (Mpc).

(Volume median diameter)
The volume median diameter (D ₅₀ ) of the toner core was measured using a Coulter Counter Multisizer 3 (manufactured by Beckman Coulter, Inc.).

<1. Raw material for preparing toner>
Next, the raw materials used for preparing the toners of Examples 1 to 12 and Comparative Examples 1 to 6 will be described.

<1-1. Preparation of amorphous polyester resin>
An amorphous polyester resin was used as the binder resin for the toner core contained in the toner. An amorphous polyester resin was prepared by the following method. A reaction vessel was charged with 1575 g of a propylene oxide adduct of bisphenol A, 163 g of an ethylene oxide adduct of bisphenol A, 377 g of fumaric acid, and 4 g of dibutyltin oxide as a catalyst. The air in the reaction vessel was replaced with a nitrogen atmosphere. Subsequently, the temperature inside the reaction vessel was increased to 220 ° C. while stirring the contents of the reaction vessel. The contents of the reaction vessel were reacted at 220 ° C. for 8 hours. Subsequently, the pressure in the reaction vessel was reduced to 60 mmHg, and the contents of the reaction vessel were further reacted for 1 hour. Thereafter, the contents of the reaction vessel were cooled to 210 ° C., and 336 g of trimellitic anhydride was added to the reaction vessel. After completion of the reaction, the contents in the reaction vessel were taken out and cooled. As a result, an amorphous polyester resin AP1 was obtained.

  Regarding the obtained amorphous polyester resin AP1, the glass transition point (Tga) was 55 ° C., the softening point (Tma) was 64 ° C., and the crystallinity index was 1.80.

<1-2. Preparation of crystalline polyester resin>
In addition to the non-crystalline polyester resin, a crystalline polyester resin was also used as the binder resin for the toner core contained in the toner. A crystalline polyester resin was prepared by the following method. A reaction vessel was charged with 132 g of 1,6-hexanediol, 230 g of 1,10-decanedicarboxylic acid, 1 g of dibutyltin oxide as a catalyst, and 0.3 g of hydroquinone. Next, the air in the reaction vessel was replaced with a nitrogen atmosphere. Subsequently, the temperature inside the reaction vessel was raised to 200 ° C. while stirring the contents of the reaction vessel. The contents of the reaction vessel were subjected to a polymerization reaction at 200 ° C. for 5 hours while distilling off by-product water. Subsequently, the pressure in the reaction vessel was reduced to 5 mmHg or more and 20 mmHg or less, and the polymerization reaction was continued. The reaction mixture was reacted at 200 ° C. until the physical properties of the reaction mixture (melting point Mpc and crystallinity index) were as shown in Table 1. As a result, crystalline polyester resins CP1, CP2, CP3, CP4, and CP5 having physical properties described in Table 1 were obtained.

  Table 1 shows melting points (Mpc) and crystallinity indices of the obtained crystalline polyester resins CP1, CP2, CP3, CP4, and CP5.

<1-3. Black colorant>
The following black colorant was used for the preparation of the toner core contained in the toner.
Black colorant B-A: carbon black, “REGAL (registered trademark) 400” manufactured by Cabot Corporation
Black colorant BB: Carbon black, “MOGUL L” manufactured by Cabot Corporation

<1-4. Color gamut adjuster>
The following color gamut adjusting agents were used for the preparation of the toner core contained in the toner.
Color gamut adjuster PA: C.I. I. Pigment Blue 15: 3 (copper phthalocyanine)
Color gamut adjuster P-B: C.I. I. Pigment Blue 15: 2
Color gamut adjuster DA: “VioletBL” manufactured by Nippon Chemical Industry Co., Ltd.

  Hereinafter, the color gamut adjuster PA, the color gamut adjuster PB, and the color gamut adjuster DA may be referred to as pigment PA, pigment PB, and dye DA, respectively. is there.

<1-5. Raw material for shell layer>
The following raw materials S1, S2, S3, and S4 were used as raw materials for the shell layer contained in the toner. The raw materials S1, S2, and S3 are raw materials for thermosetting resins. The raw material S4 is a raw material for the thermoplastic resin.

(Raw material of thermosetting resin)
Raw material S1: Methylol melamine aqueous solution (“Milben (registered trademark) Resin SM-607” manufactured by Showa Denko KK, hexamethylol melamine initial polymer aqueous solution, solid concentration 80 mass%)
Raw material S2: aqueous solution of glyoxal monomer (“BECKAMINE (registered trademark) NS-11” manufactured by DIC Corporation, solid concentration: 40 mass%)
Raw material S3: aqueous solution of methylolated urea ("Milben (registered trademark) Resin SU-100" manufactured by Showa Denko KK, solid content concentration 80 mass%)

(Raw material of thermoplastic resin)
Raw material S4: Water-soluble polyacrylamide aqueous solution (“BECKAMINE (registered trademark) A-1” manufactured by DIC Corporation, acrylamide resin aqueous solution, solid concentration 11 mass%)

<2. Preparation of toner>
Using the raw materials described above, toners of Examples 1 to 12 and Comparative Examples 1 to 6 were prepared by the following method.

[Example 1]
The toner of Example 1 was prepared by the following method. First, a toner core was prepared. The toner core of Example 1 was obtained by performing a shell layer forming step, a cleaning step, an external addition step, and a drying step on the obtained toner core. Hereinafter, the preparation of the toner core, the shell layer forming step, the cleaning step, the external addition step, and the drying step will be described.

<2-1. Preparation of toner core>
85 parts by mass of non-crystalline polyester resin AP1, 15 parts by mass of crystalline polyester resin CP1, 5 parts by mass of black colorant B-A, pigment PA (CI pigment blue 15: 3, copper phthalocyanine) 1 part by mass and 5 parts by mass of a release agent (Ester Wax, “WEP-3” manufactured by NOF Corporation) were mixed at a speed of 2400 rpm using an FM mixer (manufactured by Nippon Coke Industries, Ltd.). .

  Subsequently, the obtained mixture was subjected to a material charging speed of 5 kg / hour, a shaft rotation speed of 160 rpm, and a set temperature range of 80 ° C. to 130 ° C. using a twin screw extruder (“PCM-30” manufactured by Ikegai Co., Ltd.). Under the conditions, it was melted and kneaded. The obtained melt-kneaded product was cooled. The cooled melt-kneaded material was pulverized using a mechanical pulverizer (“Turbo Mill T250” manufactured by Freund Turbo). The obtained pulverized product was classified using an elbow jet (“EJ-LABO type” manufactured by Nippon Steel Industries, Ltd.). As a result, a toner core was obtained.

The resulting toner core had a volume median diameter (D ₅₀ ) of 6.0 μm. Next, a part of the obtained toner core was taken out. The taken-out toner core was used for the measurement of the triboelectric charge amount with the following standard carrier and the measurement of the zeta potential in the dispersion solution of pH 4 below.

(Measurement of triboelectric charge with standard carrier)
A standard carrier N-01 (standard carrier for negatively charged polar toner) provided by the Imaging Society of Japan and a toner core of 7% by mass with respect to the mass of the standard carrier are mixed with a mixing device ("Tabra (registered trademark)" manufactured by WAB. Mix for 30 minutes using a mixer "). Using the obtained mixture as a sample, the triboelectric charge amount of the toner core was measured using a Q / m meter (“MODEL 210HS-2A” manufactured by Trek).

(Measurement of zeta potential in pH 4 dispersion)
Using a magnetic stirrer, 0.2 g of toner core, 80 mL of ion-exchanged water, and 20 g of nonionic surfactant (“polyvinylpyrrolidone K-85” manufactured by Nippon Shokubai Co., Ltd., water concentration 5 mass%, solid content concentration 95 mass%) Mixed. As a result, the toner core was uniformly dispersed in a solvent (ion exchange water) to obtain a dispersion. Dilute hydrochloric acid was added to the obtained dispersion to adjust the pH of the dispersion to 4. As a result, a dispersion of a toner core having a pH of 4 was obtained. The toner core dispersion at pH 4 was used as a sample, and the zeta potential of the toner core in the dispersion was measured. The zeta potential was measured using a zeta potential / particle size distribution measuring device (“Delsa Nano HC” manufactured by Beckman Coulter, Inc.).

  With respect to the obtained toner core, the triboelectric charge amount with the standard carrier was measured by the method described above. The triboelectric charge amount of the toner core was −20 μC / g. With respect to the obtained toner core, the zeta potential in the pH 4 dispersion was measured by the method described above. The zeta potential in the toner core pH 4 dispersion was −30 mV.

  <2-2. Shell layer formation process>

  Next, using the obtained toner core and the raw material for the shell layer, a shell layer was formed on the surface of the toner core (shell layer forming step).

  The shell layer forming step was performed by the following method. 300 mL of ion-exchanged water was put into a 1 L three-necked flask equipped with a thermometer and a stirring blade. The internal temperature of the flask was kept at 30 ° C. using a water bath. Next, dilute hydrochloric acid was added to the flask to adjust the pH of the aqueous medium in the flask to 4. After adjusting to pH 4, 2 mL of methylol melamine aqueous solution (“Milben (registered trademark) resin SM-607” manufactured by Showa Denko KK, hexamethylol melamine initial polymer aqueous solution, solid content concentration 80% by mass) and water-soluble polyacrylamide 4 mL of an aqueous solution (“BECKAMINE (registered trademark) A-1” manufactured by DIC Corporation, an aqueous solution of an acrylamide resin, a solid concentration of 11% by mass) was added to the flask as a raw material for the shell layer. Next, the contents of the flask were stirred, and the raw material of the shell layer was dissolved in the aqueous medium. As a result, an aqueous solution (A) of the raw material for the shell layer was obtained.

  To the aqueous solution (A) obtained in the flask, 300 g of the toner core obtained by the preparation of the toner core described above was added. The contents of the flask were stirred for 1 hour at a speed of 200 rpm. Next, 300 mL of ion-exchanged water (aqueous medium) was added to the flask. Thereafter, the temperature inside the flask was raised to 70 ° C. at a rate of 1 ° C./min while stirring the contents of the flask at 100 rpm. After the temperature increase, the contents of the flask were continuously stirred for 2 hours under the conditions of a temperature of 70 ° C. and a speed of 100 rpm. Thereafter, sodium hydroxide was added to the flask to adjust the pH of the flask contents to 7. The flask contents were then cooled to room temperature. As a result, a dispersion (B) of toner base particles having a toner core covered with a shell layer was obtained.

<2-3. Cleaning process>
The obtained dispersion (B) of toner base particles was filtered with a Buchner funnel to obtain a wet cake of toner base particles. Next, the toner base particles were washed by dispersing the wet cake of the toner base particles in ion-exchanged water and filtering the toner base particles contained in the dispersion. The washing operation of the toner base particles with ion exchange water was repeated 5 times in the same manner.

  In the washing step, the filtrate (initial filtrate) produced when the toner mother particle dispersion (B) was filtered with a Buchner funnel was recovered as waste water. Further, a filtrate (filtrate generated by washing) generated by the washing operation of the toner mother particles 5 times with ion-exchanged water was also collected as waste water. The amount of the waste water (total amount of the recovered initial filtrate and the filtrate produced by washing) was 97 parts by mass with respect to 100 parts by mass of the toner obtained after the drying step described later. The concentration of total organic carbon (TOC) contained in the collected waste water (the collected initial filtrate and the filtrate produced by washing) was 8 mg / L. The concentration of total organic carbon in the wastewater was measured using an on-line TOC meter (“TOC-4200” manufactured by Shimadzu Corporation).

<2-4. Drying process>
The wet cake of toner base particles obtained in the washing step was dispersed in an aqueous ethanol solution having a concentration of 50% by mass to prepare a slurry. The obtained slurry was supplied to a continuous surface reformer (“Coatmizer (registered trademark)” manufactured by Freund Sangyo Co., Ltd.) to dry the toner base particles in the slurry. Drying with a coatmizer (registered trademark) was performed under conditions of a hot air temperature of 45 ° C. and a blower air volume of 2 m ³ / min.

<2-5. External process>
100 parts by mass of toner base particles dried in the drying step and 1.0 part by mass of dry silica fine particles (“AEROSIL (registered trademark) REA90” manufactured by Nippon Aerosil Co., Ltd.) as an external additive are mixed into a 10 L FM mixer. (Nippon Coke Industry Co., Ltd. "FM-10B") was mixed for 5 minutes. As a result, the external additive was adhered to the toner base particles. Thereafter, the toner was sieved with a sieve of 200 mesh (aperture 75 μm). As a result, the toner of Example 1 was obtained.

  The toner preparation method of Example 1 has been described above. Next, toners of Examples 2 to 12 and Comparative Examples 1 to 6 were prepared by the method described below.

[Example 2]
A toner of Example 2 was obtained in the same manner as in Example 1 except that the crystalline polyester resin CP2 was used instead of the crystalline polyester resin CP1.

[Example 3]
A toner of Example 3 was obtained in the same manner as in Example 1 except that the crystalline polyester resin CP3 was used instead of the crystalline polyester resin CP1.

[Example 4]
A toner of Example 4 was obtained in the same manner as Example 1 except that the following points were changed. Instead of the crystalline polyester resin CP1, a crystalline polyester resin CP2 was used. The thickness of the shell layer was changed from 20 nm to 5 nm by changing the addition amount of the raw material S1 (Milben (registered trademark) Resin SM-607) and raw material S4 (BECKAMINE (registered trademark) A-1) of the shell layer. did. The ratio of the addition amount of the shell layer material S4 (BECKAMINE (registered trademark) A-1) to the addition amount of the shell layer material S1 (Milben (registered trademark) Resin SM-607) is the same as in Example 1. It was a ratio.

[Example 5]
A toner of Example 5 was obtained in the same manner as Example 1 except that the following points were changed. Instead of the crystalline polyester resin CP1, a crystalline polyester resin CP3 was used. The thickness of the shell layer was changed from 20 nm to 50 nm by changing the addition amount of the raw material S1 (Milben (registered trademark) Resin SM-607) and the raw material S4 (BECKAMINE (registered trademark) A-1) of the shell layer. did. The ratio of the addition amount of the shell layer raw material S4 (BECKAMINE (registered trademark) A-1) to the addition amount of the shell layer raw material S1 (Milben (registered trademark) resin SM-607) is the same ratio as in Example 1. It was.

[Example 6]
A toner of Example 6 was obtained in the same manner as in Example 1, except that Pigment P-B (CI Pigment Blue 15: 2) was used instead of Pigment PA.

[Example 7]
A toner of Example 7 was obtained in the same manner as in Example 1 except that the black colorant BB was used instead of the black colorant B-A.

[Example 8]
A toner of Example 8 was obtained in the same manner as Example 1 except for the following changes. The addition amount of the black colorant B-A was changed from 5.0 parts by mass to 8.0 parts by mass. The amount of pigment PA added was changed from 1.0 part by weight to 3.0 parts by weight.

[Example 9]
A toner of Example 9 was obtained in the same manner as Example 1 except for the following changes. The addition amount of the black colorant B-A was changed from 5.0 parts by mass to 4.0 parts by mass. The amount of pigment PA added was changed from 1.0 part by mass to 0.5 part by mass.

[Example 10]
A toner of Example 10 was obtained in the same manner as in Example 1, except that the shell layer material S2 was used instead of the shell layer material S1.

[Example 11]
A toner of Example 11 was obtained in the same manner as in Example 1 except that the shell layer material S3 was used instead of the shell layer material S1.

[Example 12]
A toner of Example 12 was obtained in the same manner as in Example 1 except that the dye DA was used instead of the pigment PA.

[Comparative Example 1]
A toner of Comparative Example 1 was obtained in the same manner as in Example 1 except that no color gamut adjusting agent was used.

[Comparative Example 2]
A toner of Comparative Example 2 was obtained in the same manner as in Example 1 except that the crystalline polyester resin CP4 was used instead of the crystalline polyester resin CP1. In the toner of Comparative Example 2, toner particles are likely to aggregate in the shell layer forming step, and it is difficult to form a shell layer. For this reason, the toner of Comparative Example 2 was not evaluated later.

[Comparative Example 3]
A toner of Comparative Example 3 was obtained in the same manner as in Example 1 except that the crystalline polyester resin CP5 was used instead of the crystalline polyester resin CP1.

[Comparative Example 4]
A toner of Comparative Example 4 was obtained in the same manner as in Example 1 except that the following points were changed. The thickness of the shell layer was changed from 20 nm to 3 nm by changing the addition amount of the raw material S1 of the shell layer (Milben (registered trademark) resin SM-607) and the raw material S4 (BECKAMINE (registered trademark) A-1). did. The ratio of the addition amount of the shell layer material S4 (BECKAMINE (registered trademark) A-1) to the addition amount of the shell layer material S1 (Milben (registered trademark) Resin SM-607) is the same as in Example 1. It was a ratio.

[Comparative Example 5]
A toner of Comparative Example 5 was obtained in the same manner as in Example 1 except that the following points were changed. The thickness of the shell layer was changed from 20 nm to 55 nm by changing the addition amount of the raw material S1 of the shell layer (Milben (registered trademark) resin SM-607) and the raw material S4 (BECKAMINE (registered trademark) A-1). did. The ratio of the addition amount of the shell layer material S4 (BECKAMINE (registered trademark) A-1) to the addition amount of the shell layer material S1 (Milben (registered trademark) Resin SM-607) is the same as in Example 1. It was a ratio.

[Comparative Example 6]
In the same manner as in Example 1, a toner core was obtained. Thereafter, the shell layer forming step was not performed. The obtained toner core was used as toner base particles. The toner base particles (toner core) were subjected to a washing step, a drying step, and an external addition step in the same manner as in Example 1. As a result, the toner of Comparative Example 6 was obtained.

<3. Evaluation>
With respect to the obtained toners of Examples and Comparative Examples, the thickness of the shell layer, heat-resistant storage stability, color development, image density, fog density, and charge amount were evaluated by the following methods.

<3-1. Shell layer thickness>
The thickness of the shell layer of the toner particles contained in the toner was measured as follows. Note that a shell layer is not formed on the toner particles contained in the toner of Comparative Example 6. Therefore, for the toner of Comparative Example 6, the thickness of the shell layer was not measured.

(Method for taking TEM photograph of cross section of toner particles)
First, the 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, using a microtome (“EM UC6” manufactured by Leica Co., Ltd.) in which a diamond knife was set, a slice sample for cross-sectional observation of 200 nm thick toner particles was cut out from the obtained cured product. 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.

(Method for measuring the thickness of the shell layer)
The thickness of the shell layer was measured by analyzing a cross-sectional TEM image of the toner particles using image analysis software (“WinROOF” manufactured by Mitani Corporation). Specifically, two straight lines perpendicular to each other at substantially the center point of the cross section of the toner particle were drawn, and the lengths of four points intersecting the shell layers on the two straight lines were measured. The average value of the four lengths measured in this way was taken as the thickness of the shell layer of one toner particle to be measured. Such a measurement of the thickness of the shell layer was performed on 10 toner particles, and an average value of the thicknesses of the shell layers included in each of the 10 toner particles to be measured was obtained. The obtained average value was taken as the thickness of the shell layer provided in the toner.

  When the shell layer was less than 5 nm, it was difficult to measure the thickness of the shell layer because the interface between the shell layer and the toner core was unclear on the TEM image. Therefore, by combining TEM imaging and electron energy loss spectroscopy (EELS), mapping the element (nitrogen) characteristic of the shell layer in the TEM image, and clarifying the interface between the shell layer and the toner core The thickness of the shell layer was measured.

  Table 2 shows the measured thickness of the shell layer for the toner particles contained in the toners of Examples and Comparative Examples.

<3-2. Heat resistant storage stability>
3 g of toner was weighed into a 20 mL capacity plastic container and allowed to stand in a thermostat set at 60 ° C. for 3 hours. As a result, a toner for heat resistant storage stability evaluation was obtained. Thereafter, the toner for heat resistant storage stability evaluation was sieved using a powder tester (“TYPE PT-E 84810” manufactured by Hosokawa Micron Corporation). Specifically, according to a manual of a powder tester (manufactured by Hosokawa Micron Corporation), a toner for heat-resistant storage stability evaluation was screened using a 200-mesh screen under the conditions of rheostat scale 5 and time 30 seconds. After sieving, the mass of toner remaining on the sieve was measured. From the mass of the toner before sieving and the mass of the toner remaining on the sieving after sieving, the degree of aggregation (% by mass) was determined according to the following formula. A toner having an aggregation degree of 10% by mass or less was regarded as acceptable.

(Cohesion calculation formula)
Aggregation degree (mass%) = 100 × mass of toner remaining on sieve / mass of toner before sieving

<3-3. Preparation of two-component developer>
10 parts by mass of toner and 100 parts by mass of ferrite carrier were mixed for 30 minutes using a ball mill to obtain a two-component developer. The obtained two-component developer was used for evaluation of the following color developability, charge amount, image density (ID), and fog density (FD).

<3-4. Color development>
The resulting two-component developer was evaluated for color developability by the following method. First, an image used for evaluation was formed by the following method. A color printer (“FS-C5300DN” manufactured by Kyocera Document Solutions Inc.) was used as an evaluation machine. The prepared two-component developer was put into the black developing section of the evaluation machine, and the replenishing toner was put into the black toner container of the evaluation machine. Subsequently, an evaluation pattern was printed on a recording medium under the following conditions. Thereby, the image used for evaluation was obtained.

(Image formation conditions)
Normal temperature and humidity environment (20 ℃, 65% RH)
Linear speed: 170 mm / sec. Amount of toner loaded: 0.4 mg / cm ²
Fixing temperature: 160 ° C
Fixing pressure: 220N
Fixer nip width: 6.2 mm
Evaluation pattern: Solid image recording medium of 30 mm × 30 mm: Color / monochrome paper (“C ² ” manufactured by Fuji Xerox Co., Ltd., 70 g / m ² )

The L ^* value, a ^* value, and b ^* value of the obtained image were measured using a Macbeth reflection densitometer (“SpectroEye” manufactured by Sakata Inx Engineering Co., Ltd.).

<3-5. Image density (initial)>
An image used for evaluation was obtained in the same manner as the evaluation of color developability. The image density (ID) of the obtained image was measured using a Macbeth reflection densitometer (“SpectroEye” manufactured by Sakata Inx Engineering Co., Ltd.). A toner on which an image having an initial image density (ID) of 1.30 or more was formed was regarded as acceptable.

<3-6. Fog density (initial)>
A blank image used for evaluation was obtained by the same method as the evaluation of color development described above, except that an evaluation pattern (solid image of 30 mm × 30 mm) was printed instead of printing on a recording medium. The image density (ID) of the obtained blank paper image was measured using a Macbeth reflection densitometer (“SpectroEye” manufactured by Sakata Inx Engineering Co., Ltd.). A value obtained by subtracting the image density (ID) of the base paper from the image density (ID) of the obtained blank paper image was defined as the initial fog density (FD). A toner on which an image having an initial fog density (FD) of 0.010 or less was defined as acceptable.

<3-7. Charge amount (initial)>
The charge amount of the obtained two-component developer was measured using a Q / m meter (“MODEL 210HS-2A” manufactured by Trek). A toner having an initial charge amount of 15 μC / g or more and 35 μC / g or less was determined to be acceptable.

<3-8. Image density (after printing 10,000 sheets)>
Except for changing the evaluation pattern (solid image of 30 mm × 30 mm) to a predetermined evaluation pattern (printing rate of 5%), the predetermined evaluation pattern (printing rate of 5%) is the same as the evaluation of color development described above. Was printed on 10,000 recording media. After printing 10,000 sheets, an evaluation pattern (solid image of 30 mm × 30 mm) was printed on a recording medium by the same method as the evaluation of color development described above to obtain an image used for evaluation. The image density (ID) of the obtained image was measured using a Macbeth reflection densitometer (“SpectroEye” manufactured by Sakata Inx Engineering Co., Ltd.). A toner on which an image having an image density (ID) of 10,000 after printing 10,000 sheets was determined to be acceptable.

<3-9. Fog density (after printing 10,000 sheets)>
Except for changing the evaluation pattern (solid image of 30 mm × 30 mm) to a predetermined evaluation pattern (printing rate of 5%), the predetermined evaluation pattern (printing rate of 5%) is the same as the evaluation of color development described above. Was printed on 10,000 recording media. After printing 10,000 sheets, instead of printing an evaluation pattern (solid image of 30 mm × 30 mm) on a recording medium, a blank image used for the evaluation was obtained in the same manner as the color development evaluation described above, except that a blank sheet was printed. Obtained. The image density (ID) of the obtained blank paper image was measured using a Macbeth reflection densitometer (“SpectroEye” manufactured by Sakata Inx Engineering Co., Ltd.). The value obtained by subtracting the image density (ID) of the base paper from the image density (ID) of the obtained blank paper image was defined as the fog density (FD) after printing 10,000 sheets. A toner on which an image having a fog density (FD) of 10,000 or less after printing 10,000 sheets was determined to be acceptable.

<3-10. Charge amount (after printing 10,000 sheets)>
Except for changing the evaluation pattern (solid image of 30 mm × 30 mm) to a predetermined evaluation pattern (printing rate of 5%), the predetermined evaluation pattern (printing rate of 5%) is the same as the evaluation of color development described above. Was printed on 10,000 recording media. After printing 10,000 sheets, the two-component developer was taken out from the black color developing section of the evaluation machine. The charge amount of the two-component developer taken out was measured using a Q / m meter (“MODEL 210HS-2A” manufactured by Trek). A toner having a charge amount of 15 μC / g or more and 35 μC / g or less after printing 10,000 sheets was regarded as acceptable.

Tables 2 and 3 show the above evaluation results for the toners of the examples and comparative examples. Specifically, shell layer thickness, color developability, heat resistant storage stability, initial charge amount, initial image density, initial fog density, charge amount after printing 10,000 sheets, image density after printing 10,000 sheets , And the evaluation results of the fog density after printing 10,000 sheets. In Table 3, the L ^* value, a ^* value, and b ^* value, the initial image density, the initial fog density, the image density after printing 10,000 sheets, and the fog density after printing 10,000 sheets are shown in Table 3. Each of them shows an arithmetic average value of measurement values at five locations (a central portion and four corners of the measurement image) of the measurement image.

  In Tables 2 and 3, “Mpc” represents the melting point of the crystalline polyester resin, “ID” represents the image density, and “FD” represents the fog density. Moreover, "content of a color gamut adjusting agent" shows the addition amount (mass part) of a color gamut adjustment agent with respect to the addition amount (mass part) of a black colorant. The “first raw material” indicates a raw material of the thermosetting resin. The “second raw material” indicates a raw material for the thermoplastic resin.

  As shown in Tables 2 and 3, the toners of Examples 1 to 12 were excellent in the color development property of the formed image, the heat resistant storage stability, the charge amount, and the image density of the formed image. Even after printing 10,000 sheets, the toners of Examples 1 to 12 were excellent in the charge amount and the image density of the formed image. Further, in the images formed using the toners of Examples 1 to 12, the occurrence of fog was suppressed.

  On the other hand, in the toner of Comparative Example 1, the toner particles did not contain a color gamut adjusting facial. Therefore, the desired color developability and image density could not be obtained for the formed image.

  In the toner of Comparative Example 2, the toner particles contained a crystalline polyester resin having a low melting point. For this reason, aggregation of toner particles is likely to occur in the shell layer forming step, making it difficult to form the shell layer.

  In the toner of Comparative Example 3, the toner particles contained a crystalline polyester resin having a high melting point. Therefore, a shell layer is easily formed, and the toner of Comparative Example 4 has a relatively good heat-resistant storage stability. However, the desired image density was not obtained for the image formed with the toner of Comparative Example 4. This is presumably because the fixability of the toner was inferior due to the influence of the crystalline polyester resin having a high melting point contained in the toner particles.

  In the toner of Comparative Example 4, the shell layer of the toner particles was thin. Therefore, the toner of Comparative Example 4 tended to be inferior in heat resistant storage stability of the toner.

  The toner of Comparative Example 5 had a thick toner particle shell layer. Therefore, it was difficult to obtain desired color development and image density for the image formed with the toner of Comparative Example 6. This is presumably because the toner particle shell layer is thick and the toner fixability is poor.

  In the toner of Comparative Example 6, the toner particles did not have a shell layer. Therefore, the toner of Comparative Example 6 was inferior in the heat resistant storage stability of the toner and the charge amount of the toner after the initial printing and 10,000 sheets. In addition, fogging occurred in images formed at the initial stage and after printing 10,000 sheets.

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

DESCRIPTION OF SYMBOLS 1 Photosensitive body 6 Image forming apparatus 7 Apparatus housing 8 Paper feed part 9 Image forming part 10 Fixing part 11 Paper discharge part 12 Paper feed cassette 13 First pick-up roller 14 Paper feed roller 15 Paper feed roller 16 Paper feed roller 17 Registration roller pair 18 Second pickup roller 19 Image forming unit 20 Intermediate transfer belt 21 Secondary transfer roller 22 Black toner supply unit 23 Cyan toner supply unit 24 Magenta toner supply unit 25 Yellow toner supply unit 27 Charging unit 28 Exposure unit 29 Development Section 30 Drive roller 31 Driven roller 32 Backup roller 33 Primary transfer roller 34 Heating roller 35 Pressure roller 36 Conveying roller 37 Paper discharge tray

Claims (6)

A toner for developing an electrostatic latent image comprising a plurality of toner particles, wherein the toner particles include a toner core containing a binder resin and a colorant, and a shell layer covering the toner core,
The shell layer includes a thermosetting resin and a thermoplastic resin,
The thermosetting resin is at least one resin selected from the amino resin group consisting of melamine resin, urea resin, and glyoxal resin,
The thickness of the shell layer is 5 nm or more and 50 nm or less,
As the binder resin, including a crystalline resin and an amorphous resin,
The crystalline resin has a melting point of 50 ° C. or higher and 100 ° C. or lower,
An electrostatic latent image developing toner comprising a black colorant and a color gamut adjusting agent as the colorant.   The electrostatic latent image developing toner according to claim 1, wherein the color gamut adjusting agent is a cyan colorant.   The electrostatic latent image developing toner according to claim 1, wherein the black colorant is carbon black.   4. The electrostatic latent according to claim 1, wherein the content of the color gamut adjusting agent is 10.0% by mass or more and 40.0% by mass or less with respect to the mass of the black colorant. Toner for image development. When the electrostatic latent image developing toner is loaded on the recording medium at a dose of 0.4 mg / cm ² , an image formed by fixing the electrostatic latent image developing toner on the recording medium The electrostatic latent image according to any one of claims 1 to 4, wherein a ^* value is -4 or more and 1 or less, b ^* value is -4 or more and 1 or less, and L ^* value is 22 or less. Development toner. A method of forming an image using the electrostatic latent image developing toner according to claim 1,
A transfer step of applying a transfer bias to the recording medium such that a loading amount of the electrostatic latent image developing toner on the recording medium is 0.4 mg / cm ² ;
A fixing step of fixing the electrostatic latent image developing toner on the recording medium,
The image forming method, wherein the a ^* value of the formed image is −4 to 1 and b ^* value is −4 to 1 and L ^* value is 22 or less.

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