POLYMERIZATION TONER FOR ELECTROSTATIC DEVELOPING

A polymerization toner having superior chargeability and storage stability is provided. The polymerization toner includes a binder resin and a colorant, wherein the binder resin has a dielectric constant ranging from 2.8 to 3.7.

BEST MODE

Hereinafter, embodiments of the present invention are described in detail with examples, but the present invention is not limited to the examples.

Average Particle Size Measurement

An average particle size of toner was measured by using a Multisizer 3 Coulter Counter. An aperture of 100 μm was used in the Multisizer 3 Coulter Counter, an appropriate amount of a surfactant was added to 50 to 100 ml of ISOTON-II (Beckman Coulter Inc.) as an electrolyte, and 10 to 15 mg of a sample to be measured was added thereto, and the resultant was dispersed in a ultrasonic dispersing apparatus for 5 minutes to prepare a sample.

A glass transition temperature Tg of a sample was measured using a differential scanning calorimeter (DSC) (manufactured by Netzsch Co.) by heating the sample from 20° C. to 200° C. at a heating rate of 10° C./min, rapidly cooling the sample to a cooling rate of 10° C. at 20° C./min, and heating the sample at a heating rate of 10° C./min.

Acid Value Measurement

An acid value (mgKOH/g) was measured by dissolving a resin in dichloromethane, cooling the solution, and titrating the solution with a 0.1 N KOH methyl alcohol solution.

Molecular Weight Measurement

A molecular weight was measured by using GPC (Waters Alliance GPC 2000 Systems). Tetrahydrofuran (THF) was used as a solvent, and a calibration curve of molecular weight was obtained by using standard polystyrene.

(Preparation of Latex for Core and Shell)

A 30 L reactor equipped with a stirrer, a thermometer, and a condenser was installed in an oil bath in which oil is a heat transfer medium. 6,600 g of distilled water and 32 g of a surfactant (Dowfax 2A1) were added to the reactor, and the reactor was heated to 70° C. and stirred at 100 rpm. Then, an emulsion mixture, including monomers, i.e., 8,380 g of styrene, 3,220 g of butyl acrylate, 370 g of 2-carboxyethyl acrylate, and 226 g of 1,10-decanediol diacrylate, 5,075 g of distilled water, 226 g of the surfactant (Dowfax 2A1), 530 g of polyethylene glycol ethyl ether methacrylate, as a macro monomer, and 188 g of 1-dodecanethiol, as a chain transfer agent, was stirred at 400 rpm to 500 rpm for 30 minutes using a disc-type impeller. Then, the emulsion mixture was gradually added to the reactor for 1 hour. The reactor was maintained for about 8 hours and gradually cooled to room temperature to complete the reaction.

The glass transition temperature Tg of the binder resin measured by using a DSC was 62° C. The number-average molecular weight of the binder resin measured by GPC using polystyrene as a standard sample was 50,000. The dielectric constant of the binder resin, measured by an impedance analyzer, was 2.8.

540 g of a cyan pigment (Dainichiseika Color & Chemicals Mfg. Co., Ltd., Japan, ECB303), 27 g of a surfactant (Dowfax 2A1), and 2,450 g of distilled water were added to a 3 L reactor equipped with a stirrer, a thermometer, and a condenser, and the reactor was slowly stirred for about 10 hours to obtain a pre-dispersion. The pre-dispersion was further dispersed using a beads mill (Netzsch, Germany, Zeta RS) for 4 hours. As a result, a cyan pigment dispersion 1 was obtained.

Then, the particle size of the cyan pigment was measured using by a Multisizer 2000 (Malvern Instruments, Ltd.), and a volume-average particle diameter (D50(v)) was 170 nm. In this regard, when the volume of the particles is accumulated from particles of the smallest size in ascending order until the accumulated volume reaches 50% of the total volume of the particles, an average particle size of the accumulated particles corresponding to 50% of the total volume of the particles is defined as D50(v).

Pigment dispersions 2 to 4 were prepared by the same method as the preparation process of the pigment dispersion 1 except for using 3.7 kg of a yellow pigment (Clariant Corporation, PY74), 2.3 kg of each magenta pigment (Clariant Corporation, E02 and Sanyo Chemical Industries Ltd., PR-269), and 3.5 kg of a black pigment (Cabot Corporation, Regal 330) instead of the cyan pigment.

65 g of a surfactant (Dowfax 2A1), and 1,935 g of distilled water were added to a 5 L reactor equipped with a stirrer, a thermometer, and a condenser, and 1,000 g of wax (NOF Corporation, Japan, WE-5) was added to the reactor while slowly stirring the reactor at a high temperature for about 2 hours. The wax was dispersed for 30 minutes using a homogenizer (IKA, T-45). As a result, a wax dispersion was obtained.

Then, the particle size of the wax was measured by using a Multisizer 2000 (Malvern Instruments, Ltd.), and D50(v) was 320 nm.

13,881 g of the latex for a core, 2,238 g of the colorant dispersion, and 2,873 g of the wax dispersion were added to a 70 L reactor, and the mixture was mixed at room temperature for about 15 minutes at 1.21 m/s. 5,760 g of a solution including poly silicato iron (PSI) and nitric acid (PSI/1.88% HNO3=½), as an agglomerating agent, was added to the reactor, and then the mixture was homogenized using a homogenizer (IKA, T-45) while stirring the reactor at 25° C. at 50 rpm (at a stirring line speed of 1.79 m/sec) for 30 minutes while controlling the pH in the range of 1.3 to 2.3. After stirring the reactor for 30 minutes, the temperature of the reactor was increased to 51° C. and stirred at 2.42 m/s using a pitched paddle-type impeller having a diameter of 0.30 m and a height of 0.07 m until the D50,v, was in the range of 6.2 μm to 6.4 μm, and 5,398 g of the latex for a shell was added thereto for about 20 minutes. The reactor was stirred until an average particle size of the toner particles was in the range of 6.7 μm to 6.9 μm. A 4% sodium hydroxide aqueous solution was added to the reactor, and the reactor was stirred at 1.90 m/s until the pH reached 4 and at 1.55 m/s until the pH reached 7.0. While maintaining the stirring speed, the reactor was heated to 96° C. to fuse the toner particles. When circularity measured by using an FPIA-3000 (Sysmex Co., Japan) was 0.980, the reactor was cooled to 40° C., and the pH of the mixture was adjusted to 9.0. Then, the toner particles were isolated using an SUS sieve (pore size: 16 μm) and cleaned four times using distilled water. The pH of the toner particles was adjusted to 1.5 by using a 1.88% nitric acid aqueous solution, and the toner particles were cleaned. The toner particles were cleaned four times with distilled water to remove a surfactant or the like. Then, the cleaned toner particles were dried in a fluidized bed dryer at 40° C. for 5 hours to obtain dried toner particles.

A 3 L reactor equipped with a stirrer, a nitrogen gas inlet, a thermometer, and a cooler was installed in an oil bath in which oil is heat medium. 45 g of terephthalic acid, 39 g of isophthalic acid, 75 g of 1,2-propylene glycol, and 3 g of trimellitic acid were added to the reactor. Then, dibutyl tin oxide was added thereto as a catalyst at a ratio of 500 ppm with respect to the total weight of the monomers. Then, the reactor was heated to 150° C. while stirring the mixture of the reactor at a speed of 150 rpm. The reaction was maintained at the same temperature for about 6 hours, and the reactor was heated to 220° C. The pressure of the reactor was reduced to 0.1 torr in order to remove byproducts, and the reactor was maintained at the same pressure for 15 hours to complete the reaction. As a result, a polyester resin was obtained.

A glass transition temperature Tg of a sample was measured by using a DSC (manufactured by Netzsch Co.) by heating the sample from 20° C. to 200° C. at a heating rate 10° C./min, rapidly cooling the sample to 10° C. at a cooling rate 20° C./min, and heating the sample at a heating rate 10° C./min.

Acid Value Measurement

An acid value (mgKOH/g) was measured by dissolving a resin in dichloromethane, cooling the solution, and titrating the solution with a 0.1 N KOH methyl alcohol solution.

Measurement of Weight-Average Molecular Weight and Mp

A weight-average molecular weight of the binder resin was measured by GPC using a calibration curve for standard polystyrene samples.

A max peak position (Mp) was obtained by GPC using standard polystyrene conversion from the retention time corresponding to the peak value of the obtained elution curve. Also, the peak value of the elution curve is the point where the elution curve is a maximum, and where two maximum points exist, it is the maximum value of the elution curve. Also, the signal strength of the GPC curve at a peak molecular weight (I(Mp)) and the signal strength of the GPC curve at a molecular weight 100,000 (I(M100,000)) are, respectively, the difference between the baseline signal strength and the signal strength at a peak molecular weight and the difference between baseline signal strength and the signal strength at a molecular weight 100,000, and they are represented as potentials (mV).

Filtering Condition Sample solution was filtered by a 0.45 μm Teflon (Registered Trademark) membrane filter

The glass transition temperature Tg, the acid value, the weight-average molecular weight, and the Mp of the obtained polyester resin were 66° C., 11 mgKOH/g, 18,000, and 5100, respectively, and T1/2was 125° C. The dielectric constant of the binder resin, measured by an impedance analyzer, was 3.7.

(Preparation of Polyester Resin Dispersion)

46 g of 4 wt % sodium hydroxide solution (2.5 equivalents based on the acid value of polyester resin) as a dispersion stabilizer, 6.67 g of a surfactant (Dowfax made by Dow corning, 1 wt % based on the weight of polyester resin), and 958 g of water were added to a 3 L reactor equipped with a thermometer and an impeller type stirrer. 300 g of a solid polyester resin and 500 g of methyl ethyl ketone were added thereto, the mixture was refluxed for 1 hour at 70° C., and the mixture was nitrogen-purged for 4 hours or more at 80° C. to remove an organic solvent. As a result, a polyester resin dispersion was obtained.

3 kg of a cyan pigment (Dainichiseika Color & Chemicals Mfg. Co., Ltd., ECB303) was added to a 20 L reactor, 11.5 kg of distilled water, and 0.6 kg of hydroxypropylmethyl cellulose acetate phthalate (Samsung Fine Chemicals Co., Ltd., AnyCoat-P) were further added thereto, and the reactor was stirred at a speed of 50 rpm. Then, the mixture was transferred to a ball mill type reactor to perform a pre-dispersion. As a result of the pre-dispersion, a cyan pigment dispersion having a volume-average particle diameter (D50(v)) of 3.4 μm (measured by a multisizer coulter counter of Beckman Coulter Inc.) was obtained. Then, the contents in the reactor were subject to a high dispersion at a pressure of 1,500 bar by using an Ultimaizer system (Amstec Ltd., Model HJP25030). As a result of the high dispersion, a pigment dispersion 1 dispersed in a nano size and having a volume-average particle diameter (D50(v)) of 150 nm (measured by Microtrac 252 of Microtrac Inc.) was obtained.

Pigment dispersions 2 to 4 were prepared by the same method as the preparation process of the pigment dispersion 1 except for using 3.7 kg of a yellow pigment (Clariant Corporation, PY74), 2.3 kg of each magenta pigment (Clariant Corporation, E02 and Sanyo Chemical Industries Ltd., PR-269), and 3.5 kg of a black pigment (Cabot Corporation, Regal 330) instead of the cyan pigment.

50 g of a paraffin wax (NIPPON SEIRO, HNP10, melting point: 72° C.), 10 g of an anionic surfactant (Dow corning, Dowfax), and 160 g of an ion exchange water were put in a jacket portion, and dispersed for 30 minutes while a homogenizer (Homogenizer, IKA) was heated to 95° C. Then, the dispersion was transferred to a pressure discharge homogenizer (Homogenizer, NIPPON SEIRO), and dispersed for about 20 minutes at 90° C. As a result, a wax dispersion dispersed in a nano size and having a volume-average particle diameter (D50(v)) of 230 nm (measured by Microtrac 252 of Microtrac Inc.) was obtained.

The polyester resin dispersion, the pigment dispersion, and the wax dispersion were mixed. The mixture was heated to 53° C., and 10 g of an inorganic acid (0.3 M, nitric acid solution) and NaCl, as an agglomerating agent (4.5 wt % based on the mass of the solid contents of the reaction mixture), were added to the mixture. Then, the mixture was homogenized by using an IKA Homogenizer at 10000 rpm for 5 minutes and toner particles were aggregated. In this regard, the mass ratio of the solid contents of the polyester resin dispersion, the pigment dispersion, and the wax dispersion was 85:7:8, and the total solid contents of the reaction mixture was 13 wt %. The pH of the reaction mixture was adjusted to about 5.6 by using a 0.3 M nitric acid solution.

The average size (d50) of the obtained toner particles was 6.3±0.5 μm, and GDDv and GSDp values were 1.3 or less. The average diameter and the particle size distribution were measured by using a Coulter counter (Beckman Coulter).

Fusing was performed by adding a 1N NaOH solution by 70% of the equivalent of the agglomerating agent and stirring the mixture while the temperature for the aggregation was maintained, and then increasing the temperature to 95° C. or higher until circularity reached 0.985 or greater.

Washing and Drying Process

The toner particles were washed several times with ultrapure water until the electrical conductivity of the water after washing reaches 50 μS/cm or less, and then the pH was adjusted to 1.5 by using a 0.3M nitric acid. Then, the toner particles were again washed with ultrapure water until the electrical conductivity of the water after washing reaches 10 μS/cm or less. The wet cake of toner after the washing was dried such that the water content is 1% or less.

Comparative Example 1

Toner particles were prepared in the same manner as in Example 1, except that 330 g of 2-carboxyethyl acrylate was added instead of 370 g of 2-carboxyethyl acrylate while the latex dispersion was prepared.

Comparative Example 2

Toner particles were prepared in the same manner as in Example 1, except that 410 g of 2-carboxyethyl acrylate was added instead of 370 g of 2-carboxyethyl acrylate while the latex dispersion was prepared.

Comparative Example 3

Toner particles were prepared in the same manner as in Example 2, except that 2 g of trimellitic acid was added instead of 3 g of trimellitic acid while the polyester resin dispersion was prepared.

Comparative Example 4

Toner particles were prepared in the same manner as in Example 2, except that 4 g of trimellitic acid was added instead of 3 g of trimellitic acid while the polyester resin dispersion was prepared.

Evaluation of the toner particles prepared in Examples and Comparative Examples was performed as follows

Evaluation of Chargeability

0.5 g of toner particles prepared in Examples and Comparative Examples, and 9.5 g of a carrier (100 μm, The image society of Japan) were put in a 100 mL wide neck bottle, and left for 6 hours under an NN condition (25° C., 40%). Then, the toner particles and the carrier were mixed at 96 rpm for 60 minutes by using a Turblar mixer (WAB, Switcherland), and then the charge quantity and the charge speed were measured by using a charge quantity measuring device (TB-230, Kyosera Inc.).

Measurement of Dielectric Constant

2 g of toner particles prepared in Examples and Comparative Examples were compression-molded at a pressure of 500 kg/cm2to manufacture a sample having a diameter of 25 mm and a thickness of 2 mm. The dielectric constant was measured at 1 GHz by using an E4991A RF impedance/Material Analyzer (Agilent company).

Measurement of Storage Stability

100 g of toner particles prepared in Examples and Comparative Examples was left under an HH condition (temperature: 35° C., humidity: 50%), and the occurrence of caking was observed every 5 hours. It was evaluated that the non-occurrence of caking after left for 30 hours is OK, the occurrence of caking within 10 hours is X, and the occurrence of caking within 10 to 30 hours is A.

Evaluation of Toner Consumption

An image having a 5% of letter proportion was printed on 500 sheets of A4 paper by a Samsung CLP-510 printer using 9.75 g of toner particles prepared in Examples and Comparative Examples, weights of a developer and a waste toner were measured and compared with the weight of the initial developer to calculate the consumed amount of toner per 500 sheets.

Consumed amount of Toner per 500 sheets=(Weight of initial developer)−[(Weight of developer after printing)−(Weight of waste toner after printing)]

Image Quality Evaluation

An N2 image of JIS-JIS-SCID was printed by a Samsung CLP-510 printer using 9.75 g of toner particles prepared in Examples and Comparative Examples, and was evaluated by the following reference:

◯: Even a detailed portion of an image is viewed clearly

Δ: Slightly low

x: A detailed portion is broken

The evaluation results are shown in Tables 1 to 6.

FIG. 1is a graph showing a dielectric constant of toner particles according to Examples and Comparative Examples,FIG. 2is a graph showing charge quantity of toner particles according to Examples and Comparative Examples, andFIG. 3is a graph showing charge speed of toner particles according to Examples and Comparative Examples.

As shown in Tables 1 to 6 andFIGS. 1 to 3, the toner particles of Examples 1 and 2 according to an embodiment of the present invention have superior chargeability and storage stability, are less consumed, and have superior transfer efficiency and image quality.