Negatively-chargeable toner and method for manufacturing same

Abstract

Provided are a method for producing a negatively-chargeable toner that has a narrow particle diameter distribution even when produced by a polymerization method, and a negatively-chargeable toner that is excellent in balance between low-temperature fixability and heat-resistant shelf stability, has fine thin-line reproducibility, and generates little fog, even in high-speed printing. The negatively-chargeable toner includes colored resin particles which contain at least a binder resin, a colorant, a charge control agent and a softening agent, wherein the charge control agent is a copolymer which is obtained by copolymerizing a vinyl aromatic hydrocarbon, a (meth)acrylate and a sulfonic acid group-containing (meth)acrylamide and in which a copolymerization ratio of the sulfonic acid group-containing (meth)acrylamide is 0.8 to 4.0% by mass, and wherein the softening agent is at least one of a monoester compound and a polyglycerol ester compound.

Claims

1. A negatively-chargeable toner comprising colored resin particles which contain at least a binder resin, a colorant, a charge control agent and a softening agent, wherein the charge control agent is a copolymer which is obtained by copolymerizing a vinyl aromatic hydrocarbon, a (meth)acrylate and a sulfonic acid group-containing (meth)acrylamide and in which a copolymerization ratio of the sulfonic acid group-containing (meth)acrylamide in the copolymer is 0.8 to 4.0% by mass, and a weight average molecular weight of the charge control agent is 5,000 to 25,000, and wherein the softening agent is at least one of a monoester compound and a polyglycerol ester compound.

2. The negatively-chargeable toner according to claim 1, wherein the colorant is carbon black.

3. The negatively-chargeable toner according to claim 1, wherein an amount of the softening agent is 1 to 25 parts by mass with respect to 100 parts by mass of the binder resin.

4. The negatively-chargeable toner according to claim 1, wherein an amount of the charge control agent is 0.1 to 8 parts by mass with respect to 100 parts by mass of the binder resin.

5. The negatively-chargeable toner according to claim 1, wherein the toner is obtained by a suspension polymerization method.

6. The negatively-chargeable toner according to claim 1, wherein the negatively-chargeable toner has a core-shell structure.

7. A method for producing a negatively-chargeable toner, the method comprising: a suspension step in which, by suspending a polymerizable monomer composition which contains at least a polymerizable monomer, a colorant, a charge control agent and a softening agent in an aqueous dispersion medium which contains a dispersion stabilizer, a suspension in which droplets of the polymerizable monomer composition are dispersed is obtained, and a step of obtaining colored resin particles by carrying out suspension polymerization of the droplets of the polymerizable monomer composition in the suspension in the presence of a polymerization initiator, wherein, in the suspension step, a copolymer which is obtained by copolymerizing a vinyl aromatic hydrocarbon, a (meth)acrylate and a sulfonic acid group-containing (meth)acrylamide and in which a copolymerization ratio of the sulfonic acid group-containing (meth)acrylamide in the copolymer is 0.8 to 4.0% by mass, is used as the charge control agent, and a weight average molecular weight of the charge control agent is 5,000 to 25,000, and wherein, in the suspension step, at least one of a monoester compound and a polyglycerol ester compound is used as the softening agent.

8. The method for producing the negatively-chargeable toner according to claim 7, wherein an amount of the softening agent is 1 to 25 parts by mass with respect to 100 parts by mass of the polymerizable monomer.

9. The method for producing the negatively-chargeable toner according to of claim 7, wherein an amount of the charge control agent is 0.1 to 8 parts by mass with respect to 100 parts by mass of the polymerizable monomer.

10. The method for producing the negatively-chargeable toner according to claim 7, wherein the negatively-chargeable toner has a core-shell structure.

Description

EXAMPLES

(1) Hereinafter, the present invention will be described further in detail with reference to examples and comparative examples. Incidentally, the scope of the present invention may not be limited to the following examples. Herein, “part(s)” and (%) are based on mass if not particularly mentioned.

(2) Test methods used in the examples and the comparative examples are as follows.

EXAMPLE SERIES I

(3) I-1. Production of Sulfonic Acid Group-Containing Copolymer

Production Example I-1

(4) To a 3 L reaction vessel were charged 900 parts of toluene, 83 parts of styrene, 14.5 parts of 2-ethylhexylacrylate, 2.5 parts of 2-acrylamide-2-methylpropanesulfonic acid, and 2.4 parts of 2,2′-azobis(2,4-dimethylvaleronitrile), and a copolymerization reaction was carried out under stirring at 80° C. for 8 hours. After the reaction was completed, the solvent was removed by freeze drying, such that sulfonic acid group-containing copolymer I-1 having a weight average molecular weight of 18,000 and a glass transition temperature of 56.2° C. was obtained. The properties thereof are shown in Table I-1.

Production Examples I-2 to I-6

(5) In Production Example I-1, sulfonic acid group-containing copolymers I-2 to I-6 were each obtained in a similar manner to that of Production Example I-1, except that the use amounts of the monomers used for the copolymerization were changed as shown in the following Table I-1. The properties thereof are shown in Table I-1.

(6) The compositions and measurement results of the sulfonic acid group-containing copolymers I-1 to I-6 are shown in Table I-1. Incidentally, in the following Table I-1, “ST (wt %)” means the addition amount (% by mass) of styrene, “2EHA (wt %)” means the addition amount (% by mass) of 2-ethylhexylacrylate, and “AAMPS (wt %)” means the addition amount (% by mass) of 2-acrylamide-2-methylpropanesulfonic acid, respectively.

(7) TABLE-US-00001 TABLE I-1 Weight Glass average transition ST 2EHA AAMPS molecular temper- (wt %) (wt %) (wt %) weight ature Sulfonic acid 83 14.5 2.5 18000 56.2 group-containing copolymer I-1 Sulfonic acid 85 14 1 18000 54.6 group-containing copolymer I-2 Sulfonic acid 82 14.5 3.5 18000 55.9 group-containing copolymer I-3 Sulfonic acid 80.5 14.5 5 18000 56.6 group-containing copolymer I-4 Sulfonic acid 75 15 10 18000 56.9 group-containing copolymer I-5 Sulfonic acid 85.5 14 0.5 19000 55.6 group-containing copolymer I-6

(8) I-2. Production of Softening Agent

Production Example I-7

(9) To a reaction vessel equipped with a thermometer, a nitrogen introduction tube, an agitator, a Dean-Stark trap and a Dimroth condenser were added 100 parts of behenyl alcohol and 79.8 parts (a 1.05 molar equivalent amount of the behenyl alcohol) of stearic acid, and a reaction was carried out for 15 hours at an ordinary pressure under a nitrogen airflow at 220° C. while the water generated by the reaction was distilled off, such that an esterified crude product was obtained.

(10) To this esterified crude produce were added 20 parts of toluene and 25 parts of isopropanol, 190 parts of a 10% aqueous potassium hydroxide solution in an amount corresponding to a 1.5-fold equivalent amount of the acid value of the esterified crude product was added, and the resultant was stirred at 70° C. for 30 minutes. The resultant was allowed to stand still for 30 minutes, then the aqueous layer part was removed to complete the deacidification step. Subsequently, 20 parts of ion-exchanged water was put therein, the resultant was stirred at 70° C. for 30 minutes and then allowed to stand still for 30 minutes, and the aqueous layer part was removed. Washing with water was repeated four times until the pH of the removed aqueous layer became neutral. The solvent was distilled off by reducing the pressure of the ester layer under conditions of 180° C. and 1 kPa, and filtration was carried out to give 952.3 g of behenyl stearate, which is the final intended product. The yield with respect to the esterified crude produce subjected to the deacidification treatment was 95.2%.

Production Example I-8

(11) Pentaerythritol tetramyristate was obtained in a similar manner to the above-mentioned Production Example I-7, except that 100 parts of pentaerythritol was used instead of 100 parts of behenyl alcohol, and 704.5 parts (a 4.2 molar equivalent amount of the pentaerythritol) of myristic acid was used instead of 79.8 parts of stearic acid in Production Example I-7.

(12) I-3. Production of Negatively-Chargeable Toner

Example I-1

(13) A polymerizable monomer mixture was obtained by dispersing 75 parts of styrene and 25 parts of n-butyl acrylate as polymerizable monomers and 7 parts of carbon black (manufactured by Mitsubishi Chemical Corporation, product name: #25B) as a black colorant by using a dispersing machine (manufactured by Shinmaru Enterprises Corporation, product name: Dyno-Mill).

(14) To the above-mentioned polymerizable monomer mixture were added 0.8 part of sulfonic acid group-containing copolymer I-1 obtained in the above-mentioned Production Example I-1 as a charge control agent, 20 parts of behenyl stearate as a softening agent, 0.3 part of a polymethacrylic acid ester macromonomer (manufactured by Toagosei Co., Ltd., product name: AA6) as a macromonomer, 0.6 part of divinylbenzene as a crosslinkable polymerizable monomer, and 1.5 parts of t-dodecylmercaptan as a molecular weight modifier, and the resultant was mixed and dissolved, such that a polymerizable monomer composition was prepared.

(15) On the other hand, under room temperature, an aqueous solution in which 6.2 parts of sodium hydroxide had been dissolved in 50 parts of ion-exchanged water was gradually added to an aqueous solution in which 10.2 parts of magnesium chloride had been dissolved in 250 parts of ion-exchanged water under stirring to prepare an aqueous dispersion liquid of a magnesium hydroxide colloid (hardly water-soluble metal hydroxide colloid).

(16) The above-mentioned polymerizable monomer composition was put into the above-mentioned magnesium hydroxide colloid dispersion liquid under room temperature, and stirring was carried out. To the resultant was added 4.4 parts of a polymerization initiator (manufactured by Kayaku Akzo Corporation, product name: Trigonox 27), and high-shear stirring was carried out by using an in-line type emulsification/dispersion machine (manufactured by Pacific Machinery & Engineering Co., Ltd, product name: Cavitron) at a rotation number of 15,000 rpm for 1 minute. By this way, an aqueous dispersion liquid in which the droplets of the polymerizable monomer composition had been dispersed was prepared.

(17) The above-mentioned suspension liquid in which the droplets of the polymerizable monomer composition had been dispersed (polymerizable monomer composition dispersion liquid) was put into a reactor equipped with stirring blades, and a polymerization reaction was initiated by raising the temperature to 90° C. When the polymerization conversion reached approximately 100%, 1 part of methyl methacrylate as a polymerizable monomer for a shell and 0.3 part of 2,2′-azobis(2-methyl-N-(2-hydroxyethyl)-propionamide) as a polymerization initiator for a shell, which had been dissolved in 10 parts of ion-exchanged water, were added, the reaction was continued at 90° C. for 4 hours, and the reaction was then stopped by cooling with water, such that an aqueous dispersion liquid of colored resin particles each having a core-shell structure was obtained.

(18) Sulfuric acid was added dropwise under room temperature while the above-mentioned aqueous dispersion liquid of colored resin particles as stirred, and washing with an acid was carried out until the pH became 6.5 or less. Separation by filtration was then carried out, 500 parts of ion-exchanged water was added to the obtained solid content to form a slurry again, and treatments by water washing (washing, filtration and dehydration) were repeatedly carried out several times. Separation by filtration was then carried out, and the obtained solid content was put into a container of a drier and dried at 40° C. for 24 hours, such that core-shell type colored resin particles having a volume average particle diameter Dv of 7.8 μm and a particle diameter distribution Dv/Dn of 1.11 were obtained.

(19) To 100 parts of the dried colored resin particles were added 1.0 part of a hydrophobized negatively-chargeable silica having an average primary particle diameter of 50 nm (manufactured by Clariant) as an external additive and 0.8 part of a hydrophobized negatively-chargeable silica having an average primary particle diameter of 12 nm (manufactured by Nippon Aerosil Co., Ltd.), and an external addition treatment was carried out by conducting mixing stirring by using a laboratory scale high-speed stirring apparatus with a volume of 10 L having a cooling jacket (manufactured by Nippon Coke & Engineering Co., Ltd., product name: FM mixer) at a circumference velocity of stirring blades of 40 m/sec for an external addition treatment time of 300 seconds, such that the negatively-chargeable toner of Example I-1 was obtained. The results of the evaluation thereof are shown in Table I-2.

Examples I-2 to I-5 and Comparative Examples I-1 to I-8

(20) The negatively-chargeable toners of Examples I-2 to I-5 and Comparative Examples I-1 to I-8 were each obtained in a similar manner to that of Example I-1, except that the charge control agent and softening agent were changed as shown in Table I-2 in Example I-1. The results of the evaluation thereof are shown in Table I-2. Incidentally, in Table I-2, “FT-100” for the softening agent refers to a product name of a natural gas-based Fischer-Tropsch wax (manufactured by D Shell-MS).

(21) I-4. Evaluation of Properties of Colored Resin Particles and Toner

(22) For the above-mentioned negatively-chargeable toners of Examples I-1 to I-5 and Comparative Examples I-1 to I-8, and the colored resin particles used for these negatively-chargeable toners, the properties were investigated. The specifics are as follows.

(23) (1) Measurement of Particle Diameter of Colored Resin Particles

(24) The volume average particle diameter Dv, number average particle diameter Dn and particle diameter distribution Dv/Dn of the colored resin particles were measured by a particle diameter measuring device (manufactured by Beckman Coulter, product name: Multisizer). This measurement by a Multisizer was carried out under conditions of an aperture diameter: 100 μm, dispersion medium: Isoton II (: product name), concentration: 10%, number of measured particles: 100,000 particles.

(25) Specifically, 0.2 g of a sample of colored resin particles was put into a beaker, and an aqueous alkylbenzene sulfonate solution (manufactured by Fujifilm Corporation, product name: DryWell) was added thereto as a dispersant. Furthermore, 2 mL of a dispersion medium was added thereto to allow the colored resin particles to swell, 10 mL of a dispersion medium was added, the mixture was dispersed in an ultrasonic dispersion machine for 1 minute, and the dispersion was measured by the above-mentioned particle diameter measuring device.

(26) (2) Heat-Resistant Shelf Stability

(27) A polyethylene container of 100 mL volume was filled with 20 g of the toner, the container was then tightly-closed by sealing with a lid so that water would not enter, and the container is immersed in water in a thermostat water bath (manufactured by Yamato Scientific Co., Ltd., product name: BK300) preset to a predetermined temperature and then removed after 8 hours had passed. The toner was transferred from the removed container to a 42-mesh sieve (opening: 355 μm) so that oscillation was not applied as possible, and set into a powder body measuring device (manufactured by Hosokawa Micron, product name: Powder Tester PT-X). The amplitude of the sieve was preset to 1.0 mm, the sieve was oscillated for 30 seconds, the mass of the toner remaining on the sieve was then measured and was deemed as a mass of the aggregated toner, and the highest temperature at which the mass of the aggregated toner became 5% or less of the mass of the toner that was firstly put into the container was deemed as a heat-resistant temperature and used as an index of heat-resistant shelf stability.

(28) I-5 Evaluation of Printing with Toner

(29) Printing was evaluated for the negatively-chargeable toners of the above-mentioned Examples I-1 to I-5 and Comparative Examples I-1 to I-8. The details are as follows.

(30) (1) Minimum Fixing Temperature

(31) A fixing test was carried out by using a commercially available printer (20 papers per minute printer) of a non-magnetic one-component development system which had been modified in such a manner that the temperature of a fixing roll can be varied. The fixing test was carried out by printing a black solid-printed area (print density: 100%) and varying the temperature of the fixing roll in steps of 5° C. in the modified printer to measure the fixing rate of the toner at each temperature, thereby finding a relationship between the temperature and the fixing rate. The fixing rate was calculated from the ratio of image densities before and after a peeling operation using a tape, which was carried out against a black solid-printed area (print density: 100%) of a test paper sheet, on which printing had been made by the modified printer. Specifically, assuming that the image density before the peeling of the tape is ID (before), and the image density after the peeling of the tape is ID (after), the fixing rate can be calculated out from the following Calculation Formula 1.
(Fixing rate (%)=(ID(after)/ID(before))×100  (Calculation Formula 1)

(32) The peeling operation of the tape is a series of operation that a adhesive tape (product name: Scotch Mending Tape 810-3-18, product of Sumitomo 3M Limited) is applied to a measuring area of the test paper sheet to cause the tape to adhere to the sheet by pressing the tape under a fixed pressure, and the adhesive tape is then peeled at a fixed rate in a direction along the paper sheet. The image density was measured by means of a reflection image densitometer (manufactured by McBeth Co., product name: RD914). In this fixing test, the lowest temperature of the fixing roll at which a fixing rate of the toner was more than 80% was defined as the minimum fixing temperature of the toner.

(33) (2) Thin-Line Reproducibility

(34) For testing the thin-line reproducibility, using the same printer as that mentioned above, the toner cartridge of the developing apparatus was filled with the toner, and printing paper sheets were set.

(35) The developing apparatus was left under an environment of a normal-temperature and a normal-humidity (N/N) (temperature: 23° C., humidity: 50%) for 24 hours, and a line image was continuously formed at 2×2 dot line (width: about 85 μm) under the same environment, and the continuous printing was carried out on 10,000 sheets.

(36) The density distribution data of the line images was collected from every 500 sheets by using a printing evaluation system (manufactured by YA-MA, product name: RT2000).

(37) From the collected density distribution data of the line images, assuming that the whole width of the line of the line image at a half value of the maximum value of the density is a line width, the number of sheets on which continuous print had been carried out at which the difference of the line widths can be maintained to be 10 μm or less based on the line width formed on the firstly collected print paper was investigated.

(38) (3) Fog Test

(39) Printing paper sheets were set in a commercially available printer (28 papers per minute printer) of a non-magnetic one-component development system, the toner was put into a developing apparatus, and the developing apparatus was left under an environment of a high temperature and a high humidity (H/H) of 35° C. and a humidity of 80% RH for 24 hours and an environment of a low temperature and a low humidity (L/L) of a temperature 10° C./a relative humidity of 20% for 24 hours, respectively, and continuous printing was carried out on three sheets under the same environment at a printing density of 5%.

(40) Thereafter, white solid printing was carried out, the printing was stopped in midstream, and the toner on a non-image part on the photosensitive member after the developing was peeled off by means of a adhesive tape and then attached to a new printing paper sheet. The color tones thereof were measured by using the above-mentioned reflection image densitometer and respectively represented as coordinates on the Lab space, and a color difference ΔE was calculated and deemed as a fog value. A smaller value of this fog value indicates smaller fog.

(41) The results of the measurements and evaluations of the negatively-chargeable toners of Examples I-1 to I-5 and Comparative Examples I-1 to I-8 are shown in Table I-2. Incidentally, in the following Table I-2, “copolymerization ratio (wt %)” means each copolymerization ratio (% by mass) of 2-acrylamide-2-methylpropanesulfonic acid in the sulfonic acid group-containing copolymers I-1 to I-6. Furthermore, in the following Table I-2, “HH” in “fog” means a fog value under a high temperature-high humidity (H/H) environment in the above-mentioned fog test, and “LL” in “fog” means a fog value under a low temperature-low humidity (L/L) environment in the above-mentioned fog test.

(42) TABLE-US-00002 TABLE 2 Example I-1 Example I-2 Example I-3 Example I-4 Example I-5 Sulfonic acid group-containing Copolymer I-1 Copolymer I-2 Copolymer I-3 Copolymer I-1 Copolymer I-1 copolymer Copolymerization rate (wt %) 2.5 1 3.5 2.5 2.5 Softening Behenyl stearate 20 20 20 14 — agent (parts) Behenyl behenate — — — — 20 (parts) Pentaerythritol — — — — — tetramyristate (parts) FT-100 (parts) — — — — — Volume average particle 7.8 7.4 7.3 7.2 7.5 diameter Dv (μm) Dv/Dn 1.11 1.12 1.15 1.12 1.13 Heat resistant temperature (° C.) 56 56 56 56 56 Minimum fixing temperature 130 130 130 135 135 (° C.) Thin-line reproducibility 10000 10000 9000 10000 10000 (number of sheets) Fog HH 0.8 1.2 1.1 0.6 0.8 LL 0.3 0.4 0.6 0.3 0.4 Comparative Comparative Comparative Comparative Example I-1 Example I-2 Example I-3 Example I-4 Sulfonic acid group-containing Copolymer I-1 Copolymer I-1 Copolymer I-2 Copolymer I-3 copolymer Copolymerization rate (wt %) 2.5 2.5 1 3.5 Softening Behenyl stearate — — — — agent (parts) Behenyl behenate — — — — (parts) Pentaerythritol 10 — 10 10 tetramyristate (parts) FT-100 (parts) — 2 — — Volume average particle 7.6 7.7 7.6 7.5 diameter Dv (μm) Dv/Dn 1.16 1.20 1.17 1.23 Heat resistant temperature (° C.) 55 55 55 55 Minimum fixing temperature (° C.) 145 150 145 145 Thin-line reproducibility 8000 7000 8500 6000 (number of sheets) Fog HH 1.7 2.1 1.5 1.8 LL 1.1 1.2 0.8 1.0 Comparative Comparative Comparative Comparative Example I-5 Example I-6 Example I-7 Example I-8 Sulfonic acid group-containing Copolymer I-4 Copolymer I-5 Copolymer I-5 Copolymer I-6 copolymer Copolymerization rate (wt %) 5 10 10 0.5 Softening Behenyl stearate — — 20 20 agent (parts) Behenyl behenate — — — — (parts) Pentaerythritol 10 10 — — tetramyristate (parts) FT-100 (parts) — — — — Volume average particle 7.7 8.0 7.6 7.3 diameter Dv (μm) Dv/Dn 1.24 1.34 1.22 1.12 Heat resistant temperature (° C.) 54 54 55 56 Minimum fixing temperature (° C.) 145 150 120 130 Thin-line reproducibility 6000 4000 7000 8000 (number of sheets) Fog HH 1.9 3.1 1.7 5.5 LL 1.0 1.3 0.9 0.2

(43) I-6. Summary of Evaluation of Toners

(44) The evaluation of the toners will be considered below with referring to Tables I-1 and I-2.

(45) Firstly, the toners of Comparative Examples I-1, I-3 and I-4 will be considered. From Table I-2, these toners are toners each containing 10 parts of pentaerythritol tetramyristate as a softening agent.

(46) From Table I-2, in the toners of Comparative Examples I-1, I-3 and I-4, the heat-resistant temperature was low as 55° C. in either toner, the minimum fixing temperature was high as 145° C. in either toner, the number of the sheets for which the thin-line reproducibility was evaluated was small as 8,500 sheets or less, the value of HH fog was high as 1.5 or more, and the value of LL fog was high as 0.8 or more.

(47) It is understood from above that the toners of Comparative Examples I-1, I-3 and I-4, which contains a tetraester compound instead of a monoester compound as a softening agent are poor in heat-resistant shelf stability and low-temperature fixability, poor in thin-line reproducibility, and easily cause fog.

(48) Secondly, the toner of Comparative Example I-2 will be considered. From Table I-2, the toner of Comparative Example I-2 is a toner containing 2 parts of FT-100 as a softening agent.

(49) From Table I-2, in the toner of Comparative Example I-2, the heat-resistant temperature is low as 55° C., the minimum fixing temperature is high as 150° C., the number of the sheets for which the thin-line reproducibility was evaluated is small as 7,000, the value of HH fog is high as 2.1, and the value of LL fog is high as 1.2. Specifically, the minimum fixing temperature is the highest among the toners measured at this time.

(50) It is understood from above that the toner of Comparative Example I-2, which contains a Fischer-Tropsch wax instead of a monoester compound as a toner softening agent, is specifically poor in low-temperature fixability, poor in heat-resistant shelf stability and thin-line reproducibility, and easily causes fog.

(51) Subsequently, the toners of Comparative Examples I-5 to I-7 will be considered. From Table I-2, the toners of Comparative Examples I-5 and I-6 are toners each containing 10 parts of pentaerythritol tetramyristate as a softening agent and containing sulfonic acid group-containing copolymer I-4 or I-5 having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 5% by mass or more. Furthermore, from Table I-2, the toner of Comparative Example I-7 is a toner containing sulfonic acid group-containing copolymer I-5 having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 10% by mass.

(52) From Table I-2, the Dv/Dn of the toners of Comparative Examples I-5 to I-7 is large as 1.22 or more. This is due to that the above-mentioned copolymerization ratio exceeds 4.0% by mass, and thus a toner having homogeneous particle diameters is difficult to be obtained.

(53) Accordingly, nonhomogeneous particle diameters of the toner adversely affect, in particular, the heat-resistant shelf stability and chargeability. From Table I-2, in the toners of Comparative Examples I-5 to I-7, the heat-resistant temperature is low as 55° C. or less, the number of the sheets for which the thin-line reproducibility was evaluated is small as 7,000 sheets or less, the value of HH fog is high as 1.7 or more, and the value of LL fog is high as 0.9 or more.

(54) It is understood from the above that the toners of Comparative Examples I-5 to I-7, each contains a sulfonic acid group-containing copolymer having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of more than 4.0% by mass as a charge control agent, are poor in chargeability since homogeneous particle diameters are difficult to be obtained, and consequently, the toners are poor in heat-resistant shelf stability and thin-line reproducibility and easily cause fog.

(55) Furthermore, from Table I-2, the minimum fixing temperature is high as 145° C. or more in the toners of Comparative Examples I-5 and I-6.

(56) Accordingly, it is understood that the toners of Comparative Examples I-5 and I-6, which contain a tetraester compound as a softening agent instead of the monoester compound, are also poor in low-temperature fixability.

(57) Subsequently, the toner of Comparative Example I-8 will be considered. From Table I-2, the toner of Comparative Example I-8 is a toner containing sulfonic acid group-containing copolymer I-6 having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 0.5% by mass.

(58) From Table I-2, the toner of Comparative Example I-8 has a heat-resistant temperature of 56° C., a minimum fixing temperature of 130° C., and a value of LL fog of 0.2. Therefore, in the toner of Comparative Example I-8, no problem is seen in at least heat-resistant shelf stability, low-temperature fixability and fog under low-temperature/low-humidity (L/L) conditions. However, in the toner of Comparative Example I-8, the number of the sheets for which the thin-line reproducibility was evaluated is low as 8,000 sheets, and the value of HH fog is high as 5.5. Specifically, the value of HH fog in Comparative Example I-8 is the highest among the toners that were measured at this time.

(59) It is understood from the above that the toner of Comparative Example I-8, which contains a sulfonic acid group-containing copolymer having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of lower than 0.8% by mass as a charge control agent, is poor in thin-line reproducibility and easily causes fog.

(60) On the other hand, from Table I-2, the toners of Examples I-1 to I-5 are toners each containing any one of sulfonic acid group-containing copolymers I-1 to I-3 having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 1 to 3.5% by mass and 14 to 20 parts of behenyl stearate or 20 parts of behenyl behenate.

(61) From Table I-2, in the toners of Examples I-1 to I-5, Dv/Dn is small as 1.15 or less, the heat-resistant temperature is high as 56° C. in either case, the minimum fixing temperature is 135° C. or less, the number of the sheets for which the thin-line reproducibility was evaluated is 9,000 sheets or more, the value of HH fog is low as 1.2 or less, and the value of LL fog is low as 0.6 or less.

(62) Accordingly, it is understood that the toners of Examples I-1 to I-5, each of which contains a sulfonic acid group-containing copolymer having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 0.8 to 4.0% by mass, and contains a monoester compound as a softening agent, are toners that are excellent in balance between low-temperature fixability and heat-resistant shelf stability, have fine thin-line reproducibility, and generate little fog, even in high-speed printing.

Example Series II

(63) II-1. Production of Sulfonic Acid Group-Containing Copolymer

Production Examples II-1 to II-6

(64) Sulfonic acid group-containing copolymers II-1 to II-6 were prepared in similar manners to those for sulfonic acid group-containing copolymers I-1 to I-6 in the above-mentioned Example Series I. The compositions and physical properties of the sulfonic acid group-containing copolymers II-1 to II-6 respectively correspond to the compositions and physical properties of sulfonic acid group-containing copolymers I-1 to I-6 in the above-mentioned Table I-1.

(65) II-2. Production of Softening Agent

Production Example II-7

(66) To a reaction vessel equipped with a thermometer, a nitrogen introduction tube, an agitator, a Dean-Stark trap and a Dimroth condenser were added 100 parts of hexaglycerol and 605 parts (a 8.2 molar equivalent amount of the hexaglycerol) of behenic acid, and a reaction was carried out under a nitrogen airflow at 220° C. for 15 hours at an ordinary pressure while the water generated by the reaction was distilled off, such that an esterified crude product was obtained.

(67) To this esterified crude product were added 20 parts of toluene and 25 parts of isopropanol, and 190 parts of a 10% aqueous potassium hydroxide solution in an amount corresponding to a 1.5-fold equivalent amount of the acid value of the esterified crude product was added, and the resultant was stirred at 70° C. for 30 minutes. The resultant was allowed to stand still for 30 minute, and the aqueous layer part was removed to complete the deacidification step. Then, 20 parts of ion-exchanged water was put into the resultant, the resultant was stirred at 70° C. for 30 minutes and allowed to stand still for 30 minutes, and the aqueous layer part was then removed. Washing with water was repeated four times until the pH of the removed aqueous layer became neutral. The ester layer was subjected to a reduced pressure under conditions of 180° C. and 1 kPa to distill the solvent off, and filtration was carried out, such that hexaglycerol octabehenate, which is a final intended product, was obtained.

Production Example II-8

(68) Pentaerythritol tetramyristate was obtained in a similar manner to the above-mentioned Production Example II-7, except that 100 parts of pentaerythritol was used instead of 100 parts of hexaglycerol and 704.5 parts (a 4.2 molar equivalent amount of the pentaerythritol) of myristic acid was used instead of 605 parts of behenic acid in Production Example II-7.

(69) II-3. Production of Negatively-Chargeable Toner

Example II-1

(70) A polymerizable monomer mixture was obtained by dispersing 75 parts of styrene and 25 parts of n-butylacrylate as polymerizable monomers, and 7 parts of carbon black (manufactured by Mitsubishi Chemical Corporation, product name: #25B) as a black colorant by using a dispersing machine (manufactured by Shinmaru Enterprises Corporation, product name: Dyno-Mill).

(71) To the above-mentioned polymerizable monomer mixture were added 0.8 part of sulfonic acid group-containing copolymer II-1 obtained in the above-mentioned Production Example II-1 as a charge control agent, 5 parts of the hexaglycerol octabehenate synthesized in the above-mentioned Production Example II-7 and 5 parts of a paraffin wax having a melting point of 68° C. (manufactured by Nippon Seiro Co., Ltd., product name: HNP-11) as softening agents, 0.3 part of a polymethacrylic acid ester macromonomer (manufactured by Toagosei Co., Ltd., product name: AA6) as a macromonomer, 0.6 part of divinylbenzene as a crosslinkable polymerizable monomer, and 1 part of tetraethylthiuram disulfide as a molecular weight modifier, and the resultant was mixed and dissolved, such that a polymerizable monomer composition was prepared.

(72) On the other hand, under room temperature, an aqueous solution in which 6.2 parts of sodium hydroxide had been dissolved in 50 parts of ion-exchanged water was gradually added to an aqueous solution in which 10.2 parts of magnesium chloride had been dissolved in 250 parts of ion-exchanged water under stirring, such that an aqueous dispersion liquid of a magnesium hydroxide colloid (a hardly water-soluble metal hydroxide colloid) was prepared.

(73) The above-mentioned polymerizable monomer composition was put into the above-mentioned magnesium hydroxide colloid dispersion liquid under room temperature, and stirring was carried out. To the resultant was added 4.4 parts of a polymerization initiator (manufactured by Kayaku Akzo corporation, product name: Trigonox 27), and high-shear stirring was carried out by using an in-line type emulsification/dispersion machine (manufactured by Pacific Machinery & Engineering Co., Ltd, product name: Cavitron) at a rotation number of 15,000 rpm for 1 minute, such that fine droplets of the polymerizable monomer composition were formed in the aqueous dispersion medium. By this way, an aqueous dispersion liquid in which the droplets of the polymerizable monomer composition had been dispersed was prepared.

(74) The above-mentioned suspension liquid in which the droplets of the polymerizable monomer composition had been dispersed (polymerizable monomer composition dispersion liquid) was put into a reactor equipped with stirring blades, and a polymerization reaction was initiated by raising the temperature to 90° C. When the polymerization conversion reached about 100%, 1 part of methyl methacrylate as a polymerizable monomer for a shell, and 0.3 part of 2,2′-azobis(2-methyl-N-(2-hydroxyethyl)propionamide) as a polymerization initiator for a shell dissolved in 10 parts of ion-exchanged water, were added, the reaction was continued at 90° C. for 4 hours, and the reaction was then stopped by cooling with water, such that an aqueous dispersion liquid of colored resin particles each having a core-shell structure was obtained.

(75) Sulfuric acid was added dropwise under room temperature while the above-mentioned aqueous dispersion liquid of colored resin particles was stirred, and washing with an acid was carried out until the pH became 6.5 or less. Separation by filtration was then carried out, 500 parts of ion-exchanged water was added to the obtained solid content to form a slurry again, and treatments by water washing (washing, filtration and dehydration) were repeatedly carried out several times. Separation by filtration was then carried out, and the obtained solid content was put into a container of a drier and dried at 40° C. for 24 hours, such that core-shell type colored resin particles having a volume average particle diameter Dv of 7.8 μm and a particle diameter distribution Dv/Dn of 1.13 were obtained.

(76) To 100 parts of the dried colored resin particles were added 1.0 part of a hydrophobized negatively-chargeable silica having an average primary particle diameter of 50 nm (manufactured by Clariant) and 0.8 part of a hydrophobized negatively-chargeable silica having an average primary particle diameter of 12 nm (manufactured by Nippon Aerosil Co., Ltd.) as an external additive, and an external addition treatment was carried out by conducting mixing stirring by using a laboratory scale high-speed stirring apparatus with a volume of 10 L having a cooling jacket (manufactured by Nippon Coke & Engineering Co., Ltd., product name: FM mixer) at a circumference velocity of stirring blades of 40 m/sec for an external addition treatment time of 300 seconds, such that the negatively-chargeable toner of Example II-1 was obtained. The results of the evaluation thereof are shown in Table II-1.

Examples II-2 to II-5 and Comparative Examples II-1 to II-8

(77) The negatively-chargeable toners of Examples II-2 to II-5 and Comparative Examples II-1 to II-8 were each obtained in a similar manner to that of Example II-1, except that the negative-charging controlling resin and softening agent were changed as shown in Table II-1 in Example II-1. The results of the evaluation thereof are shown in Table II-1.

(78) II-4. Evaluation of Properties of Colored Resin Particles and Toners

(79) For the negatively-chargeable toners of the above-mentioned Examples II-1 to II-5 and Comparative Examples II-1 to II-8, the heat-resistant temperature of the toner was measured in a similar method to that in “(2) Heat-resistant shelf stability” in the above-mentioned Example Series I. Furthermore, for the colored resin particles used in these negatively-chargeable toners, the particle diameters of the colored resin particles were measured in a similar method to that in “(1) Measurement of particle diameters of colored resin particles” in the above-mentioned Example Series I.

(80) II-5. Evaluation of Printing of Toner

(81) For the negatively-chargeable toners of the above-mentioned Examples II-1 to II-5 and Comparative Examples II-1 to II-8, the printing was evaluated in similar methods to those in “(1) Minimum fixing temperature”, “(2) Thin-Line Reproducibility” and “(3) Fog Test” in the above-mentioned Example Series I. Incidentally, as to the thin-line reproducibility, “10000<” in the test result in Table II-1 indicates that the difference in line widths can be maintained at 10 μm or less even printing is continuously carried out on 10,000 sheets.

(82) Furthermore, for these negatively-chargeable toners, the durability after leaving at a high temperature was evaluated as follows.

(83) (4) Durability after Leaving at High Temperature

(84) The negatively-chargeable toner was put into a sealable container under an ordinary temperature-ordinary humidity (N/N) environment (N/N) at a temperature of 23° C. and a humidity of 50%. This container was stored under an environment at a temperature of 50° C. for 5 days, opened, and then returned to an ordinary temperature-ordinary humidity (N/N) environment (N/N) at a temperature of 23° C. and a humidity of 50%. The negatively-chargeable toner was removed from the container, and using this negatively-chargeable toner, a fog value was calculated in a similar manner to that explained in the item of “(3) Fog Test” in the above-mentioned Example Series I. The number of sheets for continuous printing for which the fog value can maintain an image quality of 1 or less was investigated. Incidentally, “10000<” in the test result of Table II-1 indicates that the fog value can maintain an image quality of 1 or less even printing is continuously carried out on 10,000 sheets.

(85) The results of the measurements and evaluations of the negatively-chargeable toners of Examples II-1 to II-5 and Comparative Examples II-1 to II-8 are shown in Table II-1. Incidentally, in the following Table II-1, “copolymerization ratio (wt %)” means each copolymerization ratio (% by mass) of 2-acrylamide-2-methylpropanesulfonic acid in sulfonic acid group-containing copolymers II-1 to II-6. Furthermore, in the following Table II-1, “HH” in “fog” means a fog value under a high temperature-high humidity (H/H) environment in the above-mentioned fog test, and “LL” in “fog” means a fog value under a low temperature-low humidity (L/L) environment in the above-mentioned fog test.

(86) TABLE-US-00003 TABLE 3 Example II-1 Example II-2 Example II-3 Example II-4 Example II-5 Sulfonic acid group-containing Copolymer II-1 Copolymer II-2 Copolymer II-3 Copolymer II-1 Copolymer II-1 copolymer Copolymerization rate (wt %)   2.5 1   3.5   2.5 2.5 Softening Hexaglycerol 5 5 5 5 10 agent octabehenate (parts) Pentaerythritol — — — — — tetramyristate (parts) Paraffin wax (parts) 5 5 5 — — Volume average particle   6.8   6.9   7.1   6.6 6.9 diameter Dv (μm) Dv/Dn   1.13   1.12   1.15   1.13 1.12 Heat resistant temperature (° C.) 56  56  56  57  55 Minimum fixing 140  140  140  145  140 temperature (° C.) Thin-line reproducibility 10000<   10000<   9000   8000   7000 (number of sheets) Fog HH   0.8   0.8   1.1   0.8 1.2 LL   0.4   0.6   0.5   0.4 0.5 Durability after leaving at high 10000<   10000<   10000<   10000<   8500 temperature (number of sheets) Comparative Comparative Comparative Comparative Example II-1 Example II-2 Example II-3 Example II-4 Sulfonic acid group-containing Copolymer II-1 Copolymer II-1 Copolymer II-2 Copolymer II-3 copolymer Copolymerization rate (wt %) 2.5 2.5 1 3.5 Softening Hexaglycerol — — — — agent octabehenate (parts) Pentaerythritol 10 — 10 10 tetramyristate (parts) Paraffin wax (parts) — 2 — — Volume average particle 7.2 6.5 7.3 7.4 diameter Dv (μm) Dv/Dn 1.18 1.20 1.17 1.23 Heat resistant temperature (° C.) 55 55 55 55 Minimum fixing 145 150 145 145 temperature (° C.) Thin-line reproducibility 8500 6000 6000 4000 (number of sheets) Fog HH 1.7 2.1 1.5 1.8 LL 1.1 1.2 0.8 1.0 Durability after leaving at high 6000 7000 8500 6000 temperature (number of sheets) Comparative Comparative Comparative Comparative Example II-5 Example II-6 Example II-7 Example II-8 Sulfonic acid group-containing Copolymer II-4 Copolymer II-5 Copolymer II-5 Copolymer II-6 copolymer Copolymerization rate (wt %) 5 10 10 05 Softening Hexaglycerol — — 6 5 agent octabehenate (parts) Pentaerythritol 10 10 — — tetramyristate (parts) Paraffin wax (parts) — — — — Volume average particle 7 7.1 6.6 6.9 diameter Dv (μm) Dv/Dn 1.24 1.34 1.22 1.12 Heat resistant temperature (° C.) 54 54 55 56 Minimum fixing 145 150 120 130 temperature (° C.) Thin-line reproducibility 7000 9500 7000 9000 (number of sheets) Fog HH 1.8 3.1 1.7 5.5 LL 1.0 1.3 0.9 0.2 Durability after leaving at high 6000 4000 7000 9500 temperature (number of sheets)

(87) II-6. Summary of Evaluation of Toners

(88) The evaluation of the toners will be considered below with mainly referring to Tables II-1.

(89) Firstly, the toners of Comparative Examples II-1, II-3 and II-4 will be considered. From Table II-1, these toners are toners each containing 10 parts of pentaerythritol tetramyristate as a softening agent.

(90) From Table II-1, in the toners of Comparative Examples II-1, II-3 and II-4, the value of HH fog is high as 1.5 or more, and the value of LL fog is high as 0.8 or more.

(91) It is understood from the above that the toners of Comparative Examples II-1, II-3 and II-4, which contain an erythritol ester compound as a softening agent instead of the polyglycerol ester compound, easily cause fog under either temperature and humidity environment.

(92) Secondly, the toner of Comparative Example II-2 will be considered. From Table II-1, the toner of Comparative Example II-2 is a toner containing only a paraffin wax (manufactured by Nippon Seiro Co., Ltd., product name: HNP-11) as a softening agent.

(93) From Table II-1, in the toner of Comparative Example II-2, the minimum fixing temperature is high as 105° C., the number of the sheets for which the thin-line reproducibility was evaluated is small as 6,000 sheets, the value of HH fog is high as 2.1, the value of LL fog is high as 1.2, and the number of the sheets for which the durability after leaving at a high temperature was evaluated is small as 7,000 sheets. Specifically, the minimum fixing temperature was the highest among the toners measured at this time.

(94) It is understood from the above that the toner of Comparative Example II-2, which contains only a paraffin wax as a softening agent, is specifically poor in low-temperature fixability, is poor in heat-resistant shelf stability, thin-line reproducibility and durability after leaving at a high temperature, and easily causes fog.

(95) Subsequently, the toners of Comparative Examples II-5 to II-7 will be considered. From Table II-1, the toners of Comparative Examples II-5 and II-6 are toners each containing 10 parts of pentaerythritol tetramyristate as a softening agent, and containing sulfonic acid group-containing copolymer II-4 or II-5 having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 5% by mass or more. Furthermore, from Table II-1, the toner of Comparative Example II-7 is a toner containing sulfonic acid group-containing copolymer II-5 having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 10% by mass.

(96) From Table II-1, the Dv/Dn of the toners of Comparative Examples II-5 to II-7 is large as 1.22 or more. This is due to that the above-mentioned copolymerization ratio is more than 4.0% by mass, and thus a toner having homogeneous particle diameters is difficult to be obtained.

(97) Therefore, the homogeneous particle diameters of the toner adversely affect, in particular the chargeability and the durability after leaving at a high temperature. From Table II-1, in the toners of Comparative Examples II-5 to II-7, the value of HH fog is high as 1.7 or more, the value of LL fog is high as 0.9 or more, and the number of the sheets for which the durability after leaving at a high temperature was evaluated is small as 7,000 sheets or less.

(98) It is understood from the above that the toners of Comparative Examples II-5 to II-7, each containing a sulfonic acid group-containing copolymer having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of more than 4.0% by mass as a charge control agent, are poor in chargeability since homogeneous particle diameters are difficult to be obtained, and consequently, the toners are poor in durability after leaving at a high temperature, and easily cause fog.

(99) Furthermore, from Table II-1, in the toners of Comparative Examples II-5 and II-6, the heat-resistant temperature is low as 54° C.

(100) Therefore, the toners of Comparative Examples II-5 and II-6, which contain an erythritol ester compound instead of a polyglycerol ester compound as a softening agent, are also poor in heat-resistant shelf stability.

(101) Subsequently, the toner of Comparative Example II-8 will be considered. From Table II-1, the toner of Comparative Example II-8 is a toner containing sulfonic acid group-containing copolymer II-6, which has a copolymerization of 2-acrylamide-2-methylpropanesulfonic acid of 0.5% by mass.

(102) From Table II-1, in the toner of Comparative Example II-8, the heat-resistant temperature is 56° C., the minimum fixing temperature is 130° C., the number of the sheets for which the thin-line reproducibility was evaluated is 9,000 sheets, the value of LL fog is 0.2, and the number of the sheets for which durability after leaving at a high temperature was evaluated is 9,500 sheets. Accordingly, in the toner of Comparative Example II-8, no problem is observed in at least the heat-resistant shelf stability, the low-temperature fixability, the thin-line reproducibility, the fog under a low temperature-low humidity (L/L) condition, and the durability after leaving at a high temperature. However, the value of HH fog is high as 5.5 in the toner of Comparative Example II-8. This value of HH fog is the highest among the toners measured at this time.

(103) From the above, it is understood that the toner of Comparative Example II-8, which contains a sulfonic cid group-containing copolymer having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of lower than 0.8% by mass as a charge control agent, easily causes fog specifically under a high temperature-high humidity environment.

(104) On the other hand, from Table II-1, the toners of Examples II-1 to II-5 are toners each containing any one of sulfonic acid group-containing copolymers II-1 to II-3, each having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 1 to 3.5% by mass, and containing hexaglycerol octabehenate.

(105) From Table II-1, in the toners of Examples II-1 to II-5, Dv/Dn is small as 1.15 or less, the heat-resistant temperature is high as 55° C. or more in either case, the minimum fixing temperature is low as 145° C. or less, the number of the sheets for which the thin-line reproducibility was evaluated is many as 7,000 sheets or more, the value of HH fog is low as 1.2 or less, the value of LL fog is low as 0.6 or less, and the number the sheets for which the durability after leaving at a high temperature was evaluated is many as 8,500 sheets or more.

(106) Accordingly, the toners of Examples II-1 to II-5, each of which contains a sulfonic acid group-containing copolymer having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 0.8 to 4.0% by mass and contains a polyglycerol ester compound as a softening agent, are toners that are excellent in balance between low-temperature fixability and heat-resistant shelf stability, have fine thin-line reproducibility, generate little fog, and are excellent in durability, even in high-speed printing.

(107) The toners of Examples II-1 to II-3 are toners further containing a paraffin wax (manufactured by Nippon Seiro Co., Ltd., product name: HNP-11) as a softening agent.

(108) From Table II-1, in the toners of Examples II-1 to II-3, the heat-resistant temperature is higher as 56° C. or more in either case, the minimum fixing temperature is lower as 140° C. or less, the number of the sheets for which the thin-line reproducibility was evaluated is larger as 9,000 sheets or more, the value of HH fog is lower as 1.1 or less, and the number of the sheets for which the durability after leaving at a high temperature was evaluated is more than 10,000 sheets in either case.

(109) Accordingly, it is understood that the toners of Examples II-1 to II-3, each contains a sulfonic acid group-containing copolymer having a copolymerization ratio of 2-acrylamide-2-methylpropanesulfonic acid of 0.8 to 4.0% by mass and further contains a polyglycerol ester compound and a paraffin wax as softening agents, are toners that are further excellent in heat-resistant shelf stability, low-temperature fixability, thin-line reproducibility, and chargeability and durability under a high temperature-high humidity (H/H) environment.

Example III-1

(110) The negatively-chargeable toner of Example III-1 was obtained in a similar manner to Example II-4, except that 14 parts of behenyl stearate was further added as a softening agent in Example II-4. When the colored resin particles and negatively-chargeable toner were evaluated in similar manners to those of Example II-4, evaluation results that were higher as a whole than those in Example II-4 were obtained. The results are shown in Table III-1. Specifically, the minimum fixing temperature in Example III-1 is 15° C. lower than the minimum fixing temperature in Example II-4. Furthermore, the number of the sheets for which the thin-line reproducibility was evaluated in Example III-1 is 2,000 sheets or more larger than the number of the sheets for which the thin-line reproducibility was evaluated in Example II-4. It is understood from the above-mentioned results that the low-temperature fixability and thin-line reproducibility of the negatively-chargeable toner of Example III-1 are further more excellent than those of Example II-4.

(111) TABLE-US-00004 TABLE III-1 Example III-1 Sulfonic acid group-containing Copolymer II-1 copolymer Copolymerization rate (wt %) 2.5 Softening Hexaglycerol octatehenate 5   agent (parts) Behenyl stearate (parts) 14   Paraffin wax (parts) — Volume average particle diameter 7.3 Dv(μm) Dv/Dn  1.11 Heat resistant temperature (° C.) 56   Minimum fixing temperature (° C.) 130    Thin-line reproducibility 10000<    (number of sheets) Fog HH 0.7 LL 0.5 Durability after leaving at high 10000<    temperature (number of sheets)