BLACK PARTICLES, BLACK COATING MATERIAL, COATING FILM, AND BLACK MATRIX FOR COLOR FILTERS

Abstract

The present invention provides black particles that have high electrical insulation and that can achieve high blackness in the visible light region, as well as a black coating material, a coating film, and a black matrix for a color filter each containing the black particles. Provided are black particles containing a copolymer including a structural unit derived from a pyrrole compound and a structural unit derived from a quinone compound, the black particles having an aqueous dispersion number average particle size of 100 nm or less and a zeta potential of −5 mV or less.

Claims

1. Black particles comprising a copolymer including a structural unit derived from a pyrrole compound and a structural unit derived from a quinone compound, the black particles having an aqueous dispersion number average particle size of 100 nm or less and a zeta potential of −5 mV or less.

2. The black particles according to claim 1, wherein the black particles contain a copolymer including a structural unit derived from pyrrole and a structural unit derived from benzoquinone.

3. A black coating material comprising the black particles according to claim 1.

4. A coating film comprising the black particles according to claim 1.

5. A black matrix for a color filter, the black matrix comprising the black particles according to claim 1.

6. A black coating material comprising the black particles according to claim 2.

7. A coating film comprising the black particles according to claim 2.

8. A black matrix for a color filter, the black matrix comprising the black particles according to claim 2.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0127] FIG. 1 shows results of solid .sup.13C-NMR of dry powder of black particles obtained in Example 1.

[0128] FIG. 2 is a FE-SEM image of an aqueous solution obtained by adding the dry powder of black particles obtained in Example 1 to a concentration of 0.1% by weight and redispersing the powder.

[0129] FIG. 3 is a FE-SEM image of an aqueous solution obtained by adding dry powder of black particles obtained in Example 2 to a concentration of 0.1% by weight and redispersing the powder.

[0130] FIG. 4 is a FE-SEM image of an aqueous solution obtained by adding dry powder of black particles obtained in Example 3 to a concentration of 0.1% by weight and redispersing the powder.

[0131] FIG. 5 is a FE-SEM image of an aqueous solution obtained by adding dry powder of black particles obtained in Example 4 to a concentration of 0.1% by weight and redispersing the powder.

[0132] FIG. 6 is a FE-SEM image of an aqueous solution obtained by adding dry powder of black particles obtained in Example 5 to a concentration of 0.1% by weight and redispersing the powder.

[0133] FIG. 7 is a FE-SEM image of an aqueous solution obtained by adding a dry product obtained in Comparative Example 1 to a concentration of 0.1% by weight and redispersing the product.

DESCRIPTION OF EMBODIMENTS

[0134] Embodiments of the present invention are more specifically described with reference to, but not limited to, examples below.

Example 1

[0135] First, 6.7 g (0.1 mol) of pyrrole (produced by Tokyo Chemical Industry Co., Ltd.) was dissolved in 1.4 L of water, to which was then added 1.75 g of formic acid (produced by Tokyo Chemical Industry Co., Ltd.), followed by stirring. Thus, an aqueous pyrrole solution was prepared.

[0136] Separately, 10.8 g (0.1 mol) of p-benzoquinone (produced by Tokyo Chemical Industry Co., Ltd.) was dissolved in a solution mixture of 0.35 L of water and 0.35 L of ethanol to prepare a p-benzoquinone solution.

[0137] The p-benzoquinone solution was dripped into the obtained aqueous pyrrole solution and mixed to prepare a mixture.

[0138] The mixture was stirred at room temperature (25° C.) for 48 hours, then heated to 60° C., and stirred for an additional 48 hours. Subsequently, the solvents (e.g., water) were removed, and the obtained product was dried at 100° C. for 16 hours and then heat-treated at 220° C. for 3 hours to prepare dry powder of black particles containing a copolymer including a structural unit derived from pyrrole and a structural unit derived from p-benzoquinone.

[0139] Here, a mixture was prepared in the same manner as above, stirred at room temperature (25° C.) for 48 hours, and then dried at 130° C. for 30 minutes. The amount of the resulting residual solids was 70% by weight or more of the amount of the pyrrole and the p-benzoquinone added. At 130° C. or higher, pyrrole and p-benzoquinone vaporize and do not remain as solids, considering the boiling point of pyrrole and the melting point (sublimation) of p-benzoquinone. The amount of residual solids after drying, however, was greater than the amount of pyrrole charged, suggesting that a copolymer of pyrrole and p-benzoquinone was obtained.

[0140] Solid .sup.13C-NMR measurement of the dry powder of black particles obtained in Example 1 gave results as shown in FIG. 1. FIG. 1 shows significant peak broadening, suggesting that the resin is not a single-structure resin. The results show that most of the carbon atoms of the resin forming the black particles are aromatic carbon and hardly include single aliphatic carbon or double-bonded carbon. This indicates that the pyrrole ring and the benzoquinone ring of the raw materials turned into a condensed ring structure to provide, for example, a copolymer having a partial structure such as one represented by the following formula (3).

##STR00003##

[0141] The obtained dry powder of black particles was added to water to a concentration of 0.1% by weight and redispersed to prepare an aqueous solution. A micrograph of the obtained aqueous solution taken using a FE-SEM is shown in FIG. 2. FIG. 2 shows that the black particles obtained in Example 1 have high dispersibility even when redispersed.

Example 2

[0142] Dry powder of black particles was obtained as in Example 1 except that phosphinic acid was used instead of formic acid.

[0143] The dry powder was redispersed to prepare an aqueous solution as in Example 1. A micrograph of the aqueous solution taken using a FE-SEM is shown in FIG. 3. FIG. 3 showed that the black particles obtained in Example 2 have high dispersibility even when redispersed.

Example 3

[0144] Dry powder of black particles was obtained as in Example 1 except that a 0.01 M aqueous hydrochloric acid solution was used instead of formic acid.

[0145] The dry powder was redispersed to prepare an aqueous solution as in Example 1. A micrograph of the aqueous solution taken using a FE-SEM is shown in FIG. 4. FIG. 4 shows that the black particles obtained in Example 3 have high dispersibility even when redispersed.

Example 4

[0146] Dry powder of black particles was obtained as in Example 1 except that citric acid was used instead of formic acid.

[0147] The dry powder was redispersed to prepare an aqueous solution as in Example 1. A micrograph of the aqueous solution taken using a FE-SEM is shown in FIG. 5. FIG. 5 shows that the black particles obtained in Example 4 have high dispersibility even when redispersed.

Example 5

[0148] Dry powder of black particles was obtained as in Example 1 except that the obtained mixture was stirred at 45° C. for 2 hours, then heated to 80° C., and stirred for an additional 48 hours.

[0149] The dry powder was redispersed to prepare an aqueous solution as in Example 1. A micrograph of the aqueous solution taken using a FE-SEM is shown in FIG. 6. FIG. 6 shows that the black particles obtained in Example 5 have high dispersibility even when redispersed.

Comparative Example 1

[0150] First, 6.7 g (0.1 mol) of pyrrole (produced by Tokyo Chemical Industry Co., Ltd.) was dissolved in 1.75 L of water, to which was then added 17.5 g of ammonium persulphate (produced by FUJIFILM Wako Pure Chemical Corporation), followed by stirring. Thus, an aqueous pyrrole solution was obtained.

[0151] The obtained aqueous pyrrole solution was stirred at room temperature (25° C.) for 48 hours, then heated to 60° C., and stirred for an additional 48 hours. The solvent (e.g., water) was then removed, and the obtained product was dried at 100° C. for 16 hours and further heat-treated at 220° C. for 3 hours, whereby a dry product was obtained. A precipitate was formed during stirring the aqueous pyrrole solution. The dry product was clumpy, and no particulate dry substance was obtained.

[0152] The dry product was redispersed to prepare an aqueous solution as in Example 1. A micrograph of the aqueous solution taken using a FE-SEM is shown in FIG. 7. FIG. 7 shows that the dry product obtained in Comparative Example 1 is clumpy and not sufficiently redispersed in water.

Comparative Example 2

[0153] Ketjen black (“EC600JD”, produced by Lion Specialty Chemicals Co., Ltd.) was used as dry powder of black particles.

Comparative Example 3

[0154] First, 1.20 g of 1,5-dihydroxynaphthalene (1,5-DHN, produced by Tokyo Chemical Industry Co., Ltd.) and 0.98 g of 1,3,5-triazine (produced by Tokyo Chemical Industry Co., Ltd.) were sequentially dissolved in 50 ml of ethanol to prepare a mixture solution in ethanol.

[0155] Next, the obtained mixture solution was stirred under heat at 80° C. for one hour (rotation rate: 300 rpm). The solution was filtered through a glass filter, and the obtained particles were washed with ethanol three times and vacuum-dried at 50° C. for three hours, followed by heating at 110° C. for two hours. Thus, dry powder of black carbon particles was obtained.

[0156] The black particles and dry product of the examples and the comparative examples were evaluated as follows. Table 1 shows the results.

Comparative Example 4

[0157] Dry powder of black particles was obtained as in Example 1 except that boric acid was used instead of formic acid.

Comparative Example 5

[0158] Dry powder of black particles was obtained as in Example 1 except that no formic acid was added.

(1) Aqueous Dispersion Number Average Particle Size

[0159] The dry powder of each of the examples and the comparative examples was added to water to prepare 10 ml of an aqueous dispersion having a concentration of 0.1% by weight. The aqueous dispersion was exposed to ultrasonic waves at 45 kHz for 30 minutes to prepare an aqueous dispersion liquid. The obtained dispersion liquid was used to measure the average particle size using a dynamic light scattering (DLS)-type particle size distribution analyzer (“Nanotrac Wave II”, produced by MicrotracBEL Corp.) under the conditions of true sphere approximation, absorption of irradiation light, and number distribution.

[0160] Comparative Example 1 was not evaluated because no dry powder was obtained.

(2) Zeta Potential

[0161] The zeta potential of the black particles of the examples and the comparative examples was measured using a micro-electrophoresis zeta potential analyzer (“MODEL 502”, produced by Nihon Rufuto Co., Ltd.). Specifically, a KCl aqueous solution (concentration: 0.01 M) was used as a support electrolyte, and a small amount of black particles were dispersed therein. The KCl solution was injected into a measurement cell. A voltage was applied thereto under observation using a microscope and adjusted until the particles stopped moving (became still). The potential at that time was taken as the zeta potential.

[0162] Comparative Example 1 was not evaluated because no dry powder was obtained.

(3) Weight Average Molecular Weight

[0163] For the black particles obtained in Examples 1 to 5 and Comparative Examples 3 to 5, the dispersion liquid obtained in “(1) Aqueous dispersion number average particle size” was analyzed using a dynamic light scattering (DLS)-type weight average molecular weight measurement device (“Nanotrac Wave II”, produced by MicrotracBEL Corp.) to measure the weight average molecular weight of the copolymer.

(4) Volume Resistivity

[0164] The volume resistivity of the black particles and the dry product of the examples and the comparative examples was measured by measuring the volume resistance value at a load of 20 kN using a powder resistivity measurement system (produced by Mitsubishi Chemical Analytech Co., Ltd.).

(5) Total Light Transmittance

[0165] A mixture of 2-hydroxyethyl methacrylate (produced by FUJIFILM Wako Pure Chemical Corporation), diallyl phthalate (produced by FUJIFILM Wako Pure Chemical Corporation), ditrimethylolpropane tetraacrylate (produced by Shin-Nakamura Chemical Co., Ltd.), and urethane acrylate (U-4HA, produced by Shin-Nakamura Chemical Co., Ltd.) at a weight ratio of 3:1:1:1 was used as a curable compound. IRGACURE 907 (produced by BASF) was used as a curing agent.

[0166] First, 45 parts by weight of the dry powder or dry product obtained in one of the examples and the comparative examples, 52.4 parts by weight of the curable compound, and 2.6 parts by weight of the curing agent were mixed at room temperature to prepare a resin composition.

[0167] The obtained resin composition was applied to a glass slide and then irradiated with ultraviolet light at 3,500 mJ/cm using a high-pressure mercury lamp to prepare a 1-μm-thick coating film. The light transmittance of the obtained coating film in the whole visible light region from 400 to 800 nm was measured at 10 points using a spectrophotometer equipped with an integrating sphere (“U-4100 type”, produced by Hitachi, Ltd.). The average transmittance and the standard deviation of the measurements at the 10 points were determined. The resin compositions obtained using the dry powders or the dry product obtained in the comparative examples were not uniform. As a result, the compositions failed to form uniform coating films, resulting in great variation in transmittance.

[0168] Here, the total light reflectance is greatly affected by the reflectance of measurement fixtures. Measuring total light transmittance thus allows more accurate measurement of the blackness of coating films.

(6) Element Content (Atom %)

[0169] The black particles and the dry product of the examples and the comparative examples were analyzed by X-ray photoelectron spectroscopy (XPS) to measure the element contents (atom %).

TABLE-US-00001 TABLE 1 Evaluation Aqueous dispersion number Total light average Weight transmittance Element content particle Zeta average Volume Standard (atom %) size potential molecular resistivity Average deviation Other (nm) (mV) weight (Ω .Math. cm) (%) (%) C N O elements Example 1 61 −45 5.8 × 10.sup.8 1 × 10.sup.7 or more 21 10 70 9 21 0 Example 2 65 −37 1.0 × 10.sup.8 1 × 10.sup.7 or more 17 8 69 8 22 1 Example 3 50 −44 1.5 × 10.sup.9 1 × 10.sup.7 or more 18 8 74 6 19 1 Example 4 72 −11 9.3 × 10.sup.8 1 × 10.sup.7 or more 22 9 72 9 17 2 Example 5 95 −27 2.8 × 10.sup.13 1 × 10.sup.7 or more 24 9 70 8 20 2 Comparative — — — 5.7 × 10.sup.4 55 33 58 13 25 4 Example 1 Comparative 177 −27 —  1.8 × 10.sup.−2 78 25 94 1 5 0 Example 2 Comparative 200 −25 6.0 × 10.sup.7 1 × 10.sup.7 or more 30 12 79 5 16 0 Example 3 Comparative 510 −2 8.9 × 10.sup.6 8.9 × 10.sup.6 66 18 69 4 20 7 Example 4 Comparative 655 14 4.1 × 10.sup.6 1 × 10.sup.7 or more 71 29 73 2 25 0 Example 5

INDUSTRIAL APPLICABILITY

[0170] The present invention can provide black particles that have high electrical insulation and that can achieve high blackness in the visible light region, as well as a black coating material, a coating film, and a black matrix for a color filter each containing the black particles.