TONER FOR ELECTROSTATIC-IMAGE DEVELOPMENT AND METHOD FOR MANUFACTURING SAME

Abstract

The present invention provides a toner for electrostatic-image development comprising color resin particle containing a binder resin, a colorant, a charge control agent, and a thickener, wherein the binder resin is a copolymer including styrene-monomer unit and (meth)acrylate monomer unit, the thickener is a resin containing a nitrogen atom, and the content of nitrogen atom is 150 to 1500 mass ppm in the toner for electrostatic-image development.

Claims

1. A toner for electrostatic-image development comprising color resin particle containing a binder resin, a colorant, a charge control agent, and a thickener. wherein the binder resin is a copolymer including styrene monomer unit and (meth)acrylate monomer unit. the thickener is a resin containing a nitrogen atom, and the content of nitrogen atom is 150 to 1500 mass ppm in the toner for electrostatic-image development.

2. The toner for electrostatic-image development according to claim 1, wherein the thickener is a resin having a urethane bond and/or a urea bond.

3. The toner for electrostatic-image development according to claim 1, wherein the thickener is a polyether resin having a methane bond and/or a urea bond.

4. The toner for electrostatic-image development according to claim 1, wherein the content of the thickener is 0.2 to 5.0 parts by mass relative to 100 parts by mass of the binder resin.

5. A toner for electrostatic-image development comprising color resin particle containing a binder resin, a colorant, and a charge control agent, wherein the binder resin is a copolymer including styrene monomer unit and (meth)acrylate monomer unit, the copolymer is cross-linked with a cross-linking agent, the cross-linking agent contains a cross-linkable resin, the cross-linkable resin is a resin containing a nitrogen atom, and the content of nitrogen atom is 150 to 1500 mass ppm in the toner for electrostatic-image development.

6. The toner for electrostatic-image development according to claim 5, wherein the cross-linkable resin is a resin having a methane bond and or a urea bond.

7. The toner for electrostatic-image development according to claim 5, wherein the cross-linkable resin is a polyether resin having a methane bond and/or a urea bond.

8. The toner for electrostatic-image development according to claim 5, wherein the cross-linkable resin is a resin having a urethane bond and an (meth)acryloyl group.

9. The toner for electrostatic-image development according to claim 5, wherein the content of the cross-linking agent is 0.3 to 5.0 parts by mass relative to 100 parts by mass of the binder resin.

10. The toner for electrostatic-image development according to claim 1, wherein tire binder resin contains 60 to 90% by mass of the styrene monomer unit and 10 to 40% by mass of the (meth)acrylate monomer unit.

11. A method for manufacturing the toner for electrostatic-image development according to claim 1, the method comprising: a step of preparing color resin particle by dispersing a polymerizable monomer composition comprising a polymerizable monomer, the colorant, the charge control agent, and the thickener and having a viscosity at 25 C. of 100 to 1000 mPa.Math.s in an aqueous dispersive medium to form a droplet, and polymerizing the droplet. wherein the polymerizable monomer includes at least a styrene monomer and an (meth)acrylate monomer, the thickener is a resin containing a nitrogen atom, and the content of nitrogen atom is 150 to 1500 mass ppm in the toner for electrostatic-image development.

12. The method for manufacturing the toner for electrostatic-image development according to claim 11, wherein the polymerizable monomer further includes a polymerizable monomer which is cross-linkable, and the amount of the polymerizable monomer which is cross-linkable to be used is 2.0 parts by mass or less in 100 parts by mass of the total amount of the polymerizable monomer.

13. A method for manufacturing the toner for electrostatic-image development according to claim 5, the method comprising: a step of preparing color resin particle by dispersing a polymerizable monomer composition comprising a polymerizable monomer, the colorant, the charge control agent, and the cross-linking agent in an aqueous dispersive medium to form a droplet, and polymerizing the droplet, wherein the polymerizable monomer includes at least a styrene monomer and an (meth)acrylate monomer. the cross-linking agent contains a cross-linkable resin, the cross-linkable resin is a resin containing a nitrogen atom, and the content of nitrogen atom is 150 to 1500 mass ppm in the toner for electrostatic-image development.

Description

EXAMPLE

[0176] Hereinafter, the present invention will be more specifically described by way of Examples and Comparative Examples, but the present invention will not be limited only to these Examples. To be noted, part(s) and % are mass-based unless otherwise specified. The test methods performed in Examples and Comparative Examples are as described below.

[0177] (1) Measurement of Nitrogen Atom Content Derived from Thickener in Toner and Nitrogen Atom Content derived from Cross-Linkable Resin in Toner

[0178] The nitrogen atom content derived from the thickener in the toner aid the nitrogen atom content derived from the cross-linkable resin in the toner were measured by a chemiluminescence method using a nitrogen analyzer. Specifically, a toner sample was thermally decomposed in the presence of a catalyst, and the nitrogen component in the toner was oxidized to obtain a nitrogen monoxide gas. The nitrogen monoxide gas was reacted with ozone to generate chemiluminescence, and the intensity of the resulting light was measured. Using a calibration curve preliminarily created, the nitrogen atom content in the toner was quantified. A difference between the nitrogen atom content in each of the toners according to Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-4 and the nitrogen atom content in the toner without, the thickener (Comparative Example 1-1) was defined as the nitrogen atom content derived from the thickener in time toner. The nitrogen atom content derived from time cross-linkable resin in the toner was calculated from a difference between the nitrogen atom content in each of the toners according to Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-3 and the nitrogen atom content in the toner without the cross-linkable resin (Comparative Example 2-1).

[0179] (2) Viscosity of Polymerizable Monomer Composition

[0180] The viscosity of the polymerizable monomer composition was treasured using a B type viscometer (available from Brookfield, model name Digital Rheometer DV-I+). Specifically, the polymerizable monomer composition was heated to 25 C. using a thermostat water bath, and a spindle was rotated at the number of rotations of the spindle of 60 rpm for one minute, followed by measurement of the viscosity. The following spindles were used according to the viscosity range for measurement:

[0181] less than 100 mPa.Math.s: spindle No.1

[0182] 100 mPa.Math.s or more and less than 200 mPa.Math.s: spindle No.2

[0183] 200 mPa.Math.s or more and less than 1500 mPa.Math.s: spindle No.3

[0184] (3) Volume Average Particle Size Dv and Particle Size Distribution Dv/Dp of Color Resin Particles

[0185] About 0.1 g of a sample (color resin particles) for measurement was weighed, and was placed into a beaker. As a dispersant, 0.1 ml of an alkylbenzene sulfonic acid aqueous solution (made by Fujifilm Corporation, trade name: Drywell) was added. Further, 10 to 30 mL of ISOTON II was added to the beaker, and the materials were dispersed for 3 minutes with a 20 W ultrasonic dispersing machine. Using a particle size analyzer (available from Beckman Coulter, Inc., trade name: Multisizer), the volume average particle size (Dv) and the number average particle diameter (Dp) of the color resin particles were measured under the conditions of an aperture diameter of 100 m, a medium of ISOTON II, and the number of particles to be measured of 100,000, and the particle size distribution (Dv/Ep) was calculated.

[0186] (4) Evaluation of Gloss

[0187] Using a commercially available non-magnetic one-component developing printer modified to change the temperature of a fixing roll unit thereof, the printer was adjusted to apply 0.30 (mg/cm.sup.2) of toner on paper for a solid image, and a solid image of a 5 cm square was printed on a paper sheet (available from Xerox Corporation, trade name: Vitality) at a temperature of the fixing roll (fixing temperature) of 170 C. The gloss of the resulting solid image of a 5 cm square was measured at an angle of incidence of 60 using a gloss meter (available from Nippon Denshoku Industries Co., Ltd., trade name: VGS-SENSOR). A greater value of the gloss indicates higher glossiness.

[0188] (5) Hot Offset Temperature

[0189] A hot offset test was performed using the same modified printer as that in (4) Evaluation of gloss above. In the hot offset test, while the temperature of the fixing roll unit was changed by 5 C. from 150 C. to 230 C., a print pattern having a solid black print region (print density: 100%) and a solid white print region (print density: 0%) was printed. When print dirt was observed in the solid white print region (print density 0%) at the corresponding temperature, visual observation was performed about the presence/absence of fusing of the toner to the fixing roll, that is, a hot offset phenomenon. In the hot offset test, the lowest setting temperature at which the fusing of the toner to the fixing roll occurred was defined as a hot offset temperature.

[0190] (6) Print Curability Test Under Normal Temperature and Normal Humidity (N/N) Environment

[0191] Using a commercially available non-magnetic one-component developing printer (resolution: 600 dpi, printing rate: 28 sheets/min), sheets of print paper were set, a toner was filled into a toner cartridge of the developing unit, and sheets of print paper were set. The printer was left to stand under a normal temperature and normal humidity (N/N) environment at a temperature of 23 C. and a humidity of 50% RH for 24 hours, and printing was continuously performed on 10000 sheets at a print density of 5% under the same environment. A solid image (print density: 100%) was printed after every 500 sheets, and the print density of the printed solid image was measured with a reflective image densitometer (available from Gretag Macbeth GmbH, trade name: RD918). Furthermore, thereafter, a solid white image (print density: 0%) was printed. The printer was stopped during the printing of the solid white image, and the toner adhering to a non-image portion on the photosensitive marker after developing was bended to an adhesive tape (available from Sumitomo 3M Limited, product name: Scotch mending tape 810-3-18), and the tape was bonded to a sheet of print paper. In the next step, the whiteness (B) of the sheet of print paper having the adhesive tape bended thereto was measured with a whiteness meter (available from Nippon Denshoku Industries Co., Ltd.). Only an unused adhesive tape was bonded to a sheet of print paper and the whiteness (A) was measured in the same manner as above. The difference (BA) in whiteness was defined as a fogging value. A smaller value indicates less fogging and better image quality.

[0192] The number of continuously printed sheets which satisfied the requirement that a print density of 1.3 or mere and a fogging value of 5 or less were maintained was examined, and evaluation was performed according to the following criteria:

[0193] A: The number of continuously printed sheets which satisfied the above requirement is 10000 or more.

[0194] B: The number of continuously printed sheets which satisfied the above requirement is 7000 or more and less than 10000.

[0195] C: The number of continuously printed sheets which satisfied the above requirement is less than 7000.

Example 1-1

[0196] 77 Parts of styrene and 23 parts of n-butyl acrylate as monovinyl monomers, 0.3 parts of divinylbenzene as a polymerizable monomer which is cross-linkable, 12 parts of carbon black (available from Mitsubishi Chemical corporation, trade name: #25B) as a black colorant, 5.0 parts of a positive-charging charge control resin (available from Fujikura Kasei Co., Ltd., trade name: FCA-676P, quaternary ammonium salt-containing styrene/acrylic resin) as a charge control agent, 1.0 part of t-dodecylmercaptan as a molecular weight adjuster, 0.1 parts of a polymethacrylic acid ester macromonomer (available from Toagosei Chemical Industry Co., Ltd., trade name: AA6, Tg: 94 C.) as a macromonomer, 20 parts of pentaerythritol tetrastearate as a release agent, and 0.5 parts (which corresponds to 0.25 parts of the polyether resin having a urea bond, and gave a content of nitrogen atom of 153 mass ppm in the toner) of a 50% dimethyl sulfoxide solution of a polyether resin having a urea bond (available from BYK Japan K.K., trade name: BYK -D410) as a thickener were mixed by stirring with a stirrer, and were further homogenously dispersed with a media-type dispersing machine to prepare a polymerizable monomer composition. The viscosity of the polymerizable monomer composition was measured according to the method described above. The viscosity of the polymerizable monomer composition is shown in Table 1.

[0197] The polyether resin having a urea bond used in Example 1-1 had a weight average molecular weight (Mw) of 1500 and a glass transition temperature (Tg) of 94.5 C.

[0198] On the other hand, under stirring at room temperature, an aqueous solution prepared by dissolving 7.0 parts of sodium hydroxide (alkali metal hydroxide) in 50 parts of deionized water was gradually added to an aqueous solution prepared by dissolving 9.0 parts of magnesium chloride (water-soluble polyvalent metal salt) in 250 parts of deionized water to prepare a magnesium hydroxide (poorly water-soluble metal hydroxide) colloidal dispersion.

[0199] The polymerizable monomer composition prepared above was added to the resulting magnesium hydroxide colloidal dispersion, and was further stirred; then, 4.4 parts of t-butyl peroxy-2-ethylbutanoate as a polymerization initiator was added thereto. Using a high speed emulsifying/dispersing machine (available from Tokushu Kika Kogyo Co., Ltd., trade name: T. K. homomixer MARK II), dispersion was performed by high speed shear stirring at a number of rotations of 12,000 rpm to form droplet of the polymerizable monomer composition.

[0200] In the next step, the aqueous dispersion of droplet of the polymerizable monomer composition was introduced from an upper portion of the reactor to perform a polymerization reaction by heating to 89 C. When the polymerization conversion ratio reached 95%, 1 part of methyl methacrylate as a polymerizable monomer for a shell and 0.1 parts of 2,2-azobis (2-methyl-N-(2-hydroxyethyl)-propionamide) as a water-soluble polymerization initiator for a shell dissolved in 10 parts of deionized water were added. The temperature was further kept at 90 C. for 3 hours to continue polymerization, and the reaction was terminated by cooling with water to prepare an aqueous dispersion of color resin particles. The proportions of the monomer unit forming the binder resin contained in the color resin particles were substantially identical to those of the introduced amounts (the same applies to Examples 1-2 to 1-7 and Comparative Examples 1-1 to 1-4 described later).

[0201] In the next, step, washing with an acid was performed by adding sulfuric acid to the aqueous dispersion of color resin particles under stirring until the pH reached 6.5 or less. The aqueous dispersion of color resin particles was filtered to separate water, and 500 parts of fresh deionized water was added to again form a slurry. The slurry was repeatedly subjected to a water-washing treatment (washing, filtration, and dehydration) at roan temperature (25 C.) several times. The resulting solids were separated through filtration, and were placed into a container of a vacuum dryer to vacuum dry the solids at a pressure of 30 torr and a temperature of 50 C. for 72 hours. Dried color resin particles were thereby-prepared. Using the color resin particles, the volume average particle size Dv and the particle size distribution Dv/Dp were measured according to the method described above. The results are shown in Table 1.

[0202] In the next step, 0.5 parts of silica fine particles subjected to hydrophobization and having a number average primary particle size of 7 ran and 1.2 parts of silica fine particles subjected to hydrophobization and having a BET specific surface area of 50 m.sup.2/g were added to 100 parts of the color resin particles prepared above, and were mixed by stirring using a high speed stirrer (available from NIPPON COKE & ENGINEERING CO., LTD., trade name: FM mixer) to perform an external addition treatment. A toner for electrostatic-image development according to Example 1-1 was thereby prepared. Using the resulting toner for electrostatic-image development, measurement of the nitrogen atom content derived from the thickener, evaluation of gloss, measurement of the hot offset temperature, and the print durability test under a normal temperature and normal humidity (N/N) environment were performed according to the methods described above. The results are shown in Table 1.

Example 1-2

[0203] A toner for electrostatic-image development was prepared in the same manner as in Example 1-1 except that the amount of the thickener was changed to 1.0 part (which corresponds to 0.5 parts of the polyether resin having a urea bond, and gave a content of nitrogen atom of 306 mass ppm in the toner), and was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

Example 1-3

[0204] A toner for electrostatic-image development was prepared in the same manner as in Example 1-1 except that the amount of the thickener was changed to 1.5 parts (which corresponds to 0.75 parts of the polyether resin having a urea bond, and gave a content of nitrogen atom of 459 mass ppm), and was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

Example 1-4

[0205] A toner for electrostatic-image development was prepared in the same manner as in Example 1-1 except that the amount of the thickener used was changed to 2.0 parts (which corresponds to 1.0 part of the polyether resin having a urea bend, and gave a content of nitrogen atom of 613 mass ppm), and was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

Example 1-5

[0206] A toner for electrostatic-image development was prepared in the same manner as in Example 1-1 except that the amount of the thickener was changed to 3.0 parts (which corresponds to 1.5 parts the polyether resin having a urea bond, and gave a content of nitrogen atom of 920 mass ppm), and was evaluated ln the same manner as in Example 1-1. The results are shown in Table 1.

Example 1-6

[0207] A toner for electrostatic-image development was prepared in the same manner as in Example 1-1 except that 4.0 parts (which corresponds to 2.0 parts of the polyether resin having a urea bond, and gave a content of nitrogen atom of 1227 mass ppm) of a 50% N-methyl-pyrrolidone solution of a polyether resin having a urea bond (available from BYK Japan K.K., trade name: BYK-410) as the thickener was used, and was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[0208] The polyether resin having a urea bond used in Example 1-6 had a weight average molecular weight (mw) of 1500 and a glass transition temperature (Tg) of 94.5 C.

Example 1-7

[0209] A toner for electrostatic-image development was prepared in the same manner as in Example 1-1 except that 3.0 parts (which corresponds to 1.5 parts of the polyether resin having a urea bond, and gave a content of nitrogen atom of 526 mass ppm) of a 50% N-methyl-2 -pyrrolidone solution of a polyether resin having a urea bond (available from BYK Japan K.K., trade name: BYK-411) was used as the thickener, and was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[0210] The polyether resin having a urea bond used in Example 1-7 had a weight average molecular weight (Mw) of 1800.

Comparative Example 1-1

[0211] A toner for electrostatic-image development was prepared in the same manner as in Example 1-1 except that, the thickener was not compounded, and was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

Comparative Example 1-2

[0212] A toner for electrostatic-image development was prepared in the same manner as in Comparative Example 1-1 except that the compounding amount of the divinylbenzene was changed to 0.6 parts, and was evaluated in the same manner as in Comparative Example 1-1. The results are shown in Table 1.

Comparative Example 1-3

[0213] A toner for electrostatic-image development was prepared in the same manner as in Example 1-1 except, that the amount of the thickener was changed to 0.2 parts (which corresponds to 0.1 parts of the polyether resin having a urea bond, and gave a content of nitrogen atom of 61 mass ppm), and was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

Comparative Example 1-4

[0214] A toner for electrostatic-image development was prepared in the same manner as in Example 1-1 except that 9.0 parts (which corresponds to 4.5 parts of the polyether resin having a urea bond, and gave a content of nitrogen atom of 1533 mass ppm) of a 50% N-methyl-2-pyrrolidone solution of a polyether resin having a urea bond (available from BYK Japan K.K., trade name: BYK-411) was used as the thickener, and was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Example Comparative Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-1 1-2 1-3 1-4 Amount of (parts) 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.6 0.3 0.3 polymerizable monomer which is cross-linkable Content of BYK-D410 (parts) 0.25 0.5 0.75 1.0 1.5 0.1 thickener BYK-410 (parts) 2.0 BYK-411 (parts) 1.5 4.5 Content of nitrogen (mass ppm) 153 306 459 613 920 1227 520 0 0 61 1533 atom derived from thickener in toner Viscosity of (mPa .Math. s) 88 230 310 370 540 980 90 48 48 62 1230 polymerizable monomer composition Volume average (m) 6.2 6.2 6.1 6.0 5.6 4.5 4.8 5.3 5.7 6.2 4.7 particle size Dv Particle size distribution Dv/Dp 1.14 1.16 1.17 1.18 1.17 1.31 1.18 1.15 1.14 1.13 1.40 Results of Gloss 6.1 6.2 5.8 5.7 6.0 5.7 5.4 5.9 2.1 5.9 evaluations Hot offset ( C.) 200 205 210 215 220 220 205 185 215 190 temperature N/N durability A A A A A B A A A A C

[0215] In Table 1, the anoint of the thickener shewn is the amount of only the thickener excluding the solvent.

[0216] (Evaluation of Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-4)

[0217] Fran Table 1, high gloss was provided and high hot offset temperature and stable fixing properties in a high temperature range, as well as favorable print durability, were demonstrated in the toners for electrostatic-image development comprising the color resin particles containing the binder resin comprising a copolymer including styrene monomer unit and (meth)acrylate monomer unit, the colorant, the charge control agent, and the resin containing a nitrogen atom as the thickener, and containing 150 to 1500 mass ppm of nitrogen atom derived from the thickener in the toner for electrostatic-image development (Examples 1-1 to 1-7).

[0218] In contrast, if the resin containing a nitrogen atom as the thickener was not compounded, the hot offset temperature was low and the fixing properties in a high temperature range were reduced (Comparative Example 1-1). If the amount of the polymerizable monomer which is cross-linkable used was increased to increase the hot offset temperature, the gloss properties were reduced although the hot offset temperature was increased (Comparative Example 1-2).

[0219] Furthermore, if the content of nitrogen atom contained in the thickener was less than 150 mass ppm, the hot offset temperature was low and the fixing properties in a high temperature range were reduced (Comparative Example 1-3). If the content of nitrogen atom contained in the thickener was more than 1500 mass ppm, the print durability was reduced (Corporative Example 1-4).

Example 2-1

[0220] 77 Parts of styrene and 23 parts of n-butyl acrylate as monovinyl monomers, 0.7 parts of a cross-linkable resin (available from NOF CORPORATION, trade name: TA-640BU2, having three (meth)acryloyl groups), which was a polyether resin having a urethane bond and (meth)acryloyl groups, as a cross-linking agent, 12 parts of carbon black (available from Mitsubishi Chemical Corporation, trade name: #25B) as a black colorant, 5.0 parts of a positive-charging charge control resin (available from Fujikura Kasei Co., Ltd., trade name: FCA-676P, quaternary ammonium salt-containing styrene/acrylic resin) as a charge control agent, 1.0 part of t-dodecylmercaptan as a molecular weight adjuster, 0.1 parts of polymethacrylic acid ester macromonomer (available from Toagosei Chemical Industry Co., Ltd., trade name: AA6, Tg: 94 C.) as a macromonomer, and 20 parts of pentaerythritol tetrastearate as a release agent were mixed by stirring with a stirrer, and were further homogeneously dispersed with a media-type dispersing machine to prepare a polymerizable monomer composition.

[0221] The polyether resin having a urethane bond and (meth)acryloyl groups used in Example 2-1 had a weight average molecular weight (Mw) of 2300.

[0222] On the other hand, under stirring at room temperature, an aqueous solution prepared by dissolving 7.0 parts of sodium hydroxide (alkali metal hydroxide) in 50 parts of deionized water was gradually added to an aqueous solution prepared by dissolving 9.0 parts of magnesium chloride (water-soluble polyvalent metal salt) in 250 parts of deionized water to prepare a magnesium hydroxide (poorly water-soluble metal hydroxide) colloidal dispersion.

[0223] The polymerizable monomer composition prepared above was added to the resulting magnesium hydroxide colloidal dispersion, and was further stirred; then, 4.4 parts of t-butyl peroxy-2-ethylbutanoate as a polymerization initiator was added thereto. Using a high speed emulsifying/dispersing machine (available from Tokushu Kika Kogyo Co., Ltd., trade name: T. K. homomixer MARK II), dispersion was performed by high speed shear stirring at a number of rotations of 12,000 rpm to form droplet of the polymerizable monomer composition.

[0224] In the next step, the aqueous dispersion of droplet of the polymerizable monomer composition was introduced from an upper portion of the reactor to perform a polymerization reaction by heating to 89 C. When the polymerization conversion ratio readied 95%, 1 part of methyl methacrylate as a polymerizable monomer for a shell and 0.1 parts of 2,2-azobis(2-methyl-N-(2 -hydroxyethyl)propionamide) as a water-soluble polymerization initiator for a shell dissolved in 10 parts of deionized water were added. The temperature was further kept at 90 C. for 3 hours to continue polymerization, and the reaction was terminated by cooling with water to prepare an aqueous dispersion of color resin particles. The proportions of the monomer unit forming the binder resin contained in the color resin particles were substantially identical to those of the introduced amounts (the same to Examples 1-2 to 1-4 and Comparative Examples 1-1 to 1-3 described later).

[0225] In the next step, washing with an acid was performed by adding sulfuric acid to the aqueous dispersion of color resin particles under stirring until the pH reached 6.5 or less. The aqueous dispersion of color resin particles was filtered to separate water, and 500 parts of fresh deionized water was added to again form a slurry. The slurry was repeatedly subjected to a water-washing treatment (washing, filtration, and dehydration) at room temperature (25 C.) several times. The resulting solids were separated through filtration, and were placed into a container of a vacuum dryer to vacuum dry the solids at a pressure of 30 torr and a temperature of 50 C. for 72 hours. Dried color resin particles were thereby prepared. Using the color resin particles, the volume average particle size Dv and the particle size distribution Dv/Dp were measured according to the method described above. The results are shown in Table 2.

[0226] In the next step, as external additives, 0.5 parts of silica fine particles subjected to hydrophobization and having a number average primary particle size of 7 nm and 1.2 parts of silica fine particles subjected to hydrophobization and having a BET specific surface area of 50 m.sup.2/g were added to 100 parts of the color resin particles prepared above, and were mixed, by stirring using a speed stirrer (available from NIPPON COKE & ENGINEERING CO., LTD., trade name: FM mixer) to perform an external addition treatment. A toner for electrostatic-image development according to Example 2-1 was thereby prepared. Using the resulting toner for electrostatic-image development, measurement of the nitrogen atom content derived from the cross-linkable resin, evaluation of gloss, and measurement of the hot offset temperature were performed, according to the methods described above. The results are shown in Table 2.

Example 2-2

[0227] A toner for electrostatic-image development was prepared in the same manner as in Example 2-1 except that the amount of the cross-linking agent used was changed to 1.0 part, and was evaluated in the same manner as in Example 2-1. The results are shown in Table 2.

Example 2-3

[0228] A toner for electrostatic-image development was prepared in the same manner as in Example 2-1 except that the amount of the cross-linking agent used was changed to 1.3 parts, and was evaluated in the same manner as in Example 2-1. The results are shown in Table 2.

Example 2-4

[0229] A toner for electrostatic-image development was prepared in the same manner as in Example 2-1 except that the amount of the cross-linking agent used was changed to 1.6 parts, and was evaluated in the same manner as in Example 2-1. The results are shown in Table 2.

Comparative Example 2-1

[0230] A toner for electrostatic-image development was prepared in the same manner as in Example 2-1 except that the cross-linkable resin as the cross-linking agent was not used and 0.3 parts of divinylbenzene as the polymerizable monomer which is cross-linkable was used, and was evaluated in the same manner as in Example 2-1. The results are shown in Table 2.

[0231] Comparative Example 2-2

[0232] A toner for electrostatic-image development was prepared in the same manner as in Comparative Example 2-1 except that the compounding amount of divinylbenzene was changed to 0.5 parts, and was evaluated in the same manner as in Example 2-1. The results are shown in Table 2.

Comparative Example 2-3

[0233] A toner for electrostatic-image development was prepared in the same manner as in Example 2-1 except that 2 parts of a cross-linkable resin (available from NIPPON SODA CO., LTD., trade name: TEAI-1000, having two (meth)acryloyl groups), which was a hydrogenated polybutadiene resin having a urethane bond and (meth)acryloyl groups, was used as the cross-linking agent, and was evaluated in the same manner as in Example 2-1. The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Example Comparative Example 2-1 2-2 2-3 2-4 2-1 2-2 2-3 Amount of TA-640BU2 (parts) 0.7 1.0 1.3 1.6 cross-linking Divinylbenzene (parts) 0.3 0.6 agent TEAI-1000 (parts) 1.9 Content of nitrogen atom (mass ppm) 306 438 569 700 0 0 287 derived from cross-linkable resin in toner Volume average partice size Dv (m) 6.8 6.7 6.8 6.1 5.3 5.4 5.4 Particle size distribution Dv/Dp 1.12 1.11 1.11 1.13 1.15 1.16 1.17 Results of Gloss 6.2 5.9 5.0 4.2 5.9 2.1 4.5 evaluations Hot offset ( C.) 205 215 215 220 185 215 185 temperature

Evaluation of Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-3

[0234] From Table 2, high gloss was provided and high hot offset temperature and stable firing properties in a high temperature range were demonstrated in the toners for electrostatic-image development comprising the color resin particles containing the binder resin comprising a copolymer including styrene monomer unit and (meth)acrylate monomer unit and cross-linked with the cross-linking agent in the specific condition, the colorant, and the charge control agent (Examples 2-1 to 2-4).

[0235] In contrast, if the binder resin comprising a copolymer cross-linked with the cross-linking agent in the specific condition was not compounded, compatibility between high gloss properties and high hot offset temperature was not obtained (Comparative Examples 2-1 and 2-2).

[0236] In Comparative Example 2-3, although the gloss properties were excellent, the hot offset temperature was reduced.