HK1064691B - Aqueous dispersion containing a complex of poly(3,4-dialkoxythiophene) and a polyanion and method for producing the same - Google Patents

Description

Aqueous dispersion containing poly (3, 4-dialkoxythiophene) and polyanion complex and method for producing same

Technical Field

The invention relates to aqueous dispersions containing poly (3, 4-dialkoxythiophene) and polyanion complexes and to a process for their preparation. The invention also relates to a coating composition containing the aqueous dispersion and a substrate containing a transparent conductive film obtained by applying the coating composition on the surface of the substrate.

Background

The transparent conductive film is used for coating transparent electrodes of liquid crystal display panels, electroluminescent display panels, plasma display panels, electrochromic display panels, solar cells, touch panels, and the like, and for coating substrates made of electromagnetic shielding materials. The most widely used transparent conductive film is an indium-doped tin oxide (i.e., ITO) film obtained using a vapor deposition method. However, the ITO film formed by the vapor deposition method has some problems such as high temperature and high cost required for film formation. The ITO film may be formed by a coating method. However, high temperature is required for film formation by this method, the conductivity of the film depends on the degree of dispersion of ITO, and the haze value of the film is not always low. In addition, in the case of an inorganic oxide film such as an ITO film, cracks tend to be generated in bending the substrate, thereby decreasing the conductivity.

On the other hand, it has been proposed to use, as a transparent conductive film made of an organic material, a transparent conductive film made of a conductive polymer that can be produced at a low temperature and at a low production cost. As for the conductive polymer that can be used for the preparation of such a transparent conductive film, japanese laid-open patent No. jp2636968 discloses a complex of poly (3, 4-dialkoxythiophene) and a polyanion and a preparation method of the complex. The composite has good water dispersibility. The film produced by applying the coating composition containing the aqueous composite dispersion to a substrate has a sufficient antistatic effect, but is insufficient in transparency and conductivity.

Japanese laid-open patent No. jp8-48858 describes a thin film having improved conductivity, which is produced by applying a coating composition onto a substrate, wherein the coating polymer is obtained by adding a compound selected from a compound having two or more hydroxyl groups, a compound having an amide group, or a compound having a lactam group, to an aqueous dispersion containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion described in japanese patent specification No. jp 2636968. Japanese laid-open patent No. JP2000-153229 describes a film having improved conductivity, which is produced by applying a coating composition containing an aprotic compound having a dielectric constant ε.gtoreq.15 to a substrate and drying the resulting substrate at a temperature of less than 100 ℃.

The properties of all coating compositions described in these publications can be improved by adding a specific compound to aqueous dispersions containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion as described in Japanese patent No. JP2636968, while the electrical conductivity of these coating compositions is relatively improved. However, the aqueous dispersion containing the composite (i.e., the conductive polymer) is the same, and thus the transparency and conductivity of the film obtained from the aqueous dispersion are still insufficient.

The present invention has been made to solve the above problems, and an object thereof is to develop an aqueous dispersion containing a conductive polymer capable of forming a conductive film having excellent transparency and conductivity, and a coating composition containing the same.

To solve these problems, the inventors of the present invention have found through intensive studies that an aqueous dispersion containing a conductive polymer having excellent transparency and conductivity can be obtained by using peroxodisulfuric acid as an oxidizing agent in the presence of a polyanion or by using an arbitrary oxidizing agent in combination with an acid for lowering the pH at the time of polymerization of (3, 4-dialkoxythiophene), thereby completing the present invention.

Disclosure of Invention

The present invention provides a process for producing an aqueous dispersion containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion, which comprises: polymerizing 3, 4-dialkoxythiophene represented by the formula (1):

wherein R is¹And R²Independently is hydrogen or C_1-4Alkyl, or together form a C which may optionally be substituted_1-4Alkylene, wherein the polymerization is carried out in an aqueous solvent in the presence of the polyanion by using peroxodisulfuric acid as an oxidizing agent.

The present invention provides a process for producing an aqueous dispersion containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion, which comprises: chemically oxidatively polymerizing 3, 4-dialkoxythiophene represented by the formula (1):

wherein R is¹And R²Independently is hydrogen or C_1-4Alkyl, or together form a C which may optionally be substituted_1-4Alkylene, wherein the polymerization is carried out in an aqueous solvent by using an oxidizing agent in the presence of the polyanion, wherein an acid selected from the group consisting of water-soluble inorganic acids and water-soluble organic acids is added for lowering the pH of the resulting reaction mixture.

The present invention provides a process for producing an aqueous dispersion containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion, which comprises: polymerizing 3, 4-dialkoxythiophene represented by the formula (1):

wherein R is¹And R²Independently of hydrogenOr C_1-4Alkyl, or together form a C which may optionally be substituted_1-4Alkylene, wherein the polymerization is carried out in an aqueous solvent in the presence of the polyanion by using peroxodisulfuric acid as an oxidizing agent, wherein an acid selected from the group consisting of water-soluble inorganic acids and water-soluble organic acids is added for lowering the pH of the resulting reaction mixture.

The present invention also provides aqueous dispersions containing poly (3, 4-dialkoxythiophene) and polyanions prepared by the process described above.

The invention also provides a coating composition comprising an aqueous dispersion containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion, said compound being selected from the group consisting of water-soluble amide group-containing compounds, water-soluble hydroxyl group-containing compounds, water-soluble sulfoxides, and water-soluble sulfones.

The present invention also provides a substrate having a transparent conductive film, which is obtained by applying the above-mentioned coating composition on the surface of a substrate and drying the resultant substrate.

Hereinafter, the present invention will be described in detail.

The process for preparing an aqueous dispersion of a complex containing poly (3, 4-dialkoxythiophene) and a polyanion according to the present invention comprises: polymerizing 3, 4-dialkoxythiophene represented by the formula (1):

wherein R is¹And R²Independently is hydrogen or C_1-4Alkyl, or together form a C which may optionally be substituted_1-4Alkylene, wherein the polymerization is carried out in an aqueous solvent in the presence of the polyanion by using peroxodisulfuric acid as an oxidizing agent, or by using an oxidizing agent in an aqueous solvent, to which is added a compound selected from the group consisting of water-soluble inorganic acids and water-soluble organic acidsFor lowering the pH of the resulting reaction mixture.

In 3, 4-dialkoxythiophenes, with R¹And R²Is represented by C_1-4Preferred examples of the alkyl group include methyl, ethyl and n-propyl. From R¹And R²Co-formed of C_1-4Examples of alkylene groups include 1, 2-alkylene and 1, 3-alkylene groups, preferably methylene, 1, 2-ethylene and 1, 3-propylene groups. Of these groups, 1, 2-alkylene is particularly preferred. C_1-4The alkylene group may be optionally substituted, and examples of the substituent include C_1-12Alkyl groups and phenyl groups. Substituted C_1-4Examples of alkylene groups include 1, 2-cyclohexylene and 2, 3-butylene. A typical example of an alkylene group is represented by R¹And R²The 1, 2-alkylene group co-formed being bound by a C_1-12Alkyl substitution. Such 1, 2-alkylene groups may be derived from 1, 2-dibromoalkanes, which may be produced by bromination of alpha-olefins, such as ethylene, propylene, hexene, octene, dodecene or styrene.

Examples of the polyanion used in the above-mentioned method include polycarboxylic acids such as polyacrylic acid, polymethacrylic acid and polymaleic acid; polysulfonic acids, such as polystyrenesulfonic acid and polyvinylsulfonic acid. Among these acids, polystyrene sulfonic acid is particularly preferable. The polycarboxylic acid may be a copolymer of a vinyl carboxylic acid and another polymerizable monomer, and the polysulfonic acid may be a copolymer of a vinyl sulfonic acid and another polymerizable monomer. Examples of the polymerizable monomer include acrylates and styrenes. The number average molecular weight of the polyanion is preferably 1000-. The polyanion is used in an amount of preferably 50 to 3000 parts by weight, more preferably 100 to 1000 parts by weight, and most preferably 150 to 500 parts by weight, relative to 100 parts by weight of thiophene.

Accordingly, in one embodiment, the present invention provides a process for producing an aqueous dispersion containing a complex of poly (3, 4-ethylenedioxythiophene) and a polyanion, the process comprising: polymerizing 3, 4-dialkoxythiophene represented by the formula (1):

wherein R is¹And R²Independently is hydrogen or C_1-4Alkyl, or together form a C which may optionally be substituted_1-4An alkylene group, wherein the polymerization reaction is carried out in an aqueous solvent by using peroxodisulfuric acid as an oxidizing agent in the presence of a polyanion, and the polyanion includes a polycarboxylic acid or a polysulfonic acid.

The solvent used in the above process is an aqueous solvent, with water being particularly preferred. In addition, water containing a water-miscible solvent such as alcohol compounds (e.g., methanol, ethanol, 2-propanol, and 1-propanol), acetone, and acetonitrile can be used.

Examples of the oxidizing agent used in the polymerization of the 3, 4-dialkoxythiophene in the process of the present invention include, but are not limited to, peroxodisulfuric acid, sodium peroxodisulfate, potassium peroxodisulfate, ammonium peroxodisulfate, inorganic salts of iron oxide (e.g., iron (III) salts of inorganic acids), organic salts of iron oxide (e.g., iron (III) salts of organic acids), hydrogen peroxide, potassium permanganate, potassium dichromate, alkali perborate salts, and copper salts. Of these oxidizing agents, peroxodisulfuric acid, sodium peroxodisulfate, potassium peroxodisulfate and ammonium peroxodisulfate are most preferred. The amount of the oxidizing agent to be used is preferably 1 to 5 equivalents, more preferably 2 to 4 equivalents, relative to 1 mole of thiophene.

In the process of the present invention, it is preferred that the pH of the reaction mixture during the polymerization reaction is low (preferably 1.5 or less). Therefore, when peroxodisulfuric acid is selected from the above-mentioned oxidizing agents, it is sufficient for the preferred application to simply add it to the reaction system without adjusting the pH. When other oxidizing agents are selected, it is necessary to add an acid to adjust the pH. The pH of the reaction mixture is preferably 1.5 or less, more preferably 1.0 or less.

As the above acid, one selected from water-soluble inorganic acids and water-soluble organic acids can be used. Examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. Examples of the organic acid include p-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid and trifluoromethanesulfonic acid.

In addition, if desired, catalytic amounts of metal ions, such as iron, cobalt, nickel, molybdenum and vanadium ions (or compounds which can form these metal ions), can be added as oxidizing agents.

In order to suppress side reactions, the temperature of the reaction mixture during the polymerization in the present process is 0 to 100 ℃, preferably 0 to 50 ℃, more preferably 0 to 30 ℃.

The polymerization reaction may be carried out for 5 to 100 hours, and usually for 10 to 40 hours, depending on the type and amount of the oxidizing agent, the polymerization reaction temperature, the pH of the reaction mixture, and the like.

The polymerization reaction produces poly (3, 4-dialkoxythiophene). This polymerization reaction is carried out in the presence of a polyanion, and thus poly (3, 4-dialkoxythiophene) is complexed with this polyanion, and is therefore referred to as "a complex of poly (3, 4-dialkoxythiophene) and a polyanion" or simply "a complex" in this specification.

In addition to the aqueous dispersion containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion, the coating composition of the present invention may contain a compound selected from the group consisting of: water-soluble compounds containing amide groups, water-soluble compounds containing hydroxyl groups, water-soluble sulfoxide compounds and water-soluble sulfone compounds. The purpose of adding such a compound or compounds is to improve the conductivity of the coating film.

Examples of the water-soluble compound having an amide group included in the coating composition of the present invention include, but are not limited to, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-methylformamide, N-dimethylformamide, and formamide. Lactone-type compounds such as gamma-butyrolactone have substantially the same effects as those of water-soluble compounds having an amide group. Among these compounds, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-methylformamide, formamide and N, N-dimethylformamide are preferable. The most preferred compound is N-methylformamide. These amide compounds may be used alone or in combination of two or more.

Preferred examples of the water-soluble hydroxyl group-containing compound contained in the coating composition of the present invention include polyhydric alcohols such as glycerin, 1, 3-butanediol, ethylene glycol and diethylene glycol monoethyl ether. They may be used alone or in combination of two or more.

Examples of the water-soluble sulfoxide compound contained in the coating composition of the present invention include dimethyl sulfoxide and diethyl sulfoxide.

Examples of the water-soluble sulfone compound contained in the coating composition of the present invention include diethyl sulfone and tetramethylene sulfone.

The coating compound of the present invention may contain a water-soluble or water-dispersible binder resin in order to improve film formability and adhesion to a substrate. Examples of the water-soluble or water-dispersible binder resin include, but are not limited to, polyesters, poly (meth) acrylic acids, polyurethanes, polyvinyl acetates, polyvinylidene chlorides, polyamides, polyimides, copolymers containing a copolymerization component selected from styrene, vinylidene chloride, vinyl chloride and alkyl (meth) acrylates.

The coating compound of the present invention may contain a small amount of a surfactant in order to improve wettability to a substrate. Preferred examples of the surfactant include, but are not limited to, nonionic surfactants (e.g., polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, sorbitan fatty acid esters, fatty acid alcohol amides), fluorocarbon surfactants (e.g., fluoroalkyl carboxylic acids, perfluoroalkyl benzene sulfonic acids, perfluoroalkyl quaternary ammonium salts, and perfluoroalkyl polyoxyethylene alcohols).

In addition, the coating compound of the present invention may contain water or a water-miscible solvent in order to improve wettability to a substrate and drying property of a coating film. Examples of the water-miscible solvent include, but are not limited to, methanol, ethanol, 2-propanol, n-propanol, isobutanol, ethylene glycol, propylene glycol, acetone, methyl ethyl ketone, acetonitrile, tetrahydrofuran, dioxane, and a mixed solvent of these compounds.

Examples of substrates that can be coated using the coating compounds of the present invention include plastic sheets, plastic films, nonwoven fabrics, and glass sheets. Examples of the plastic constituting the plastic sheet or film include polyester, polystyrene, polyimide, polyamide, polysulfone, polycarbonate, polyvinyl chloride, polyethylene, polypropylene, a mixture of these polymers, a copolymer containing a monomer constituting these polymers, a phenol resin, an epoxy resin, and an ABS resin.

Examples of suitable coating methods include, but are not limited to, coating techniques such as gravure coating, roll coating, rod coating; printing techniques such as screen printing, gravure printing, flexography, offset printing and inkjet printing; spraying; and dip coating.

By applying the coating composition to a substrate and drying the substrate, a film (i.e., a transparent conductive film) is formed on the surface of the substrate. The coating liquid is dried at 20-250 ℃ for 3 seconds to one week, preferably at 70-130 ℃ for 5-60 seconds.

Thus, the coated substrate having a transparent conductive film of the present invention is obtained. The film thus obtained on the surface of the substrate has flexibility and significantly improved transparency and conductivity, as compared with conventional films prepared using polythiophene conductive polymer.

The transparent conductive film is preferably used in the following devices: surface electrodes of electroluminescent displays, pixel electrodes of liquid crystal displays, capacitive electrodes, various transparent electrodes such as transparent electrodes of touch screens, and electromagnetic shielding of cathode ray tube displays.

Drawings

FIG. 1 shows the relationship between total light transmittance and surface resistivity of a coated substrate obtained by the method of the invention.

Detailed Description

Examples

Hereinafter, the present invention will be described more specifically by way of examples and comparative examples. However, the present invention is not limited to these examples. It should be noted that the term "parts" in the following examples and comparative examples means "parts by weight".

1. The materials used

In these examples and comparative examples, VERSA-TL72 (number average molecular weight: 75000, solid content: 20%) produced by Nippon NSC Ltd. was diluted and used as an aqueous solution of polystyrenesulfonic acid for producing an aqueous dispersion containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion.

The ion exchange treatment of the aqueous dispersion of poly (3, 4-dialkoxythiophene) and a polyanion was carried out using Lewatit S100H manufactured by BAYER AG as the cation exchange resin and Lewatit MP62 manufactured by BAYER AG as the anion exchange resin.

In these examples and comparative examples, Gabsen ES-210 (solid content: 25%) manufactured by Nagase Chemtex Corporation was used as an aqueous polyester resin dispersion used as a bonding component of the coating composition. Pluscoat RY-2 (solid content: 10%) manufactured by Goo Chemical Co., Ltd. was used as the fluorocarbon surfactant.

2. Coating and drying method

In these examples and comparative examples, the coating composition was coated on a substrate and dried in the following manner. A PET film (lumirror t-60 produced by Toray industries, inc.) was used as a substrate, and the coating composition was coated on the substrate using a wire bar [ No.8 (for preparing a coating layer having a thickness of 18.3 μm under wet conditions), No.12 (for preparing a coating layer having a thickness of 27.4 μm under wet conditions), or No.16 (for preparing a coating layer having a thickness of 36.6 μm under wet conditions) ], and dried by air blowing at 100 ℃ for 1 to 3 minutes, thereby obtaining a coated substrate with a thin film.

3. Evaluation of a film on the surface of a substrate in these examples and comparative examples

3.1 surface resistivity was measured in accordance with JIS K6911 using Loresta-GP (MCP-T600) manufactured by Mitsubishi Chemical Corporation.

3.2 Total light transmittance and haze value were measured according to JIS K7150 using haze computer HGM-2B manufactured by SUGA Test Instruments Co.Ltd. The untreated PET film (Lumiror T type: Toray) had a total light transmittance of 87.8% and a haze value of 1.9%.

3.3 the adhesion of the coating film to the substrate was measured in accordance with the lattice pattern cutting test of JIS K5400.

Example 1

First, 49 parts of an aqueous solution of 1% iron (III) sulfate, 8.8 parts of 3, 4-ethylenedioxythiophene and 117 parts of an aqueous solution of 10.9% peroxodisulfuric acid are added to 1887 parts of an aqueous solution containing 20.8 parts of polystyrenesulfonic acid. The pH of the reaction mixture at this point was 1.34. The reaction mixture was stirred at 18 ℃ for 23 hours. Then, 154 parts of cation exchange resin and 232 parts of anion exchange resin were added to the reaction mixture and stirred for 2 hours. Next, the ion exchange resin was filtered off to obtain a deionized aqueous dispersion (2041 parts: solid content 1.32%) containing poly (3, 4-ethylenedioxythiophene) and polystyrenesulfonic acid.

Comparative example 1

First, 49 parts of an aqueous solution of 1% iron (III) sulfate, 8.8 parts of 3, 4-ethylenedioxythiophene and 17.4 parts of sodium peroxodisulfate were added to 2012 parts of an aqueous solution containing 22.2 parts of polystyrenesulfonic acid. The pH of the reaction mixture at this point was 1.52. The reaction mixture was stirred at 18 ℃ for 23 hours. Then, 154 parts of cation exchange resin and 232 parts of anion exchange resin were added to the reaction mixture and stirred for 2 hours. Next, the ion exchange resin was filtered off to obtain a deionized aqueous dispersion (2066 parts: solid content 1.37%) containing poly (3, 4-ethylenedioxythiophene) and polystyrenesulfonic acid.

Example 2

First, 49 parts of a 1% aqueous solution of iron (III) sulfate, 64.2 parts of a 25% aqueous solution of sulfuric acid, 8.8 parts of 3, 4-ethylenedioxythiophene and 17.4 parts of sodium peroxodisulfate were added to 1964 parts of an aqueous solution containing 22.2 parts of polystyrenesulfonic acid. The pH of the reaction mixture at this point was 0.93. The reaction mixture was stirred at 18 ℃ for 23 hours. Then, 154 parts of cation exchange resin and 232 parts of anion exchange resin were added to the reaction mixture and stirred for 2 hours. Next, the ion exchange resin was filtered off to obtain a deionized aqueous dispersion (2082 parts: solid content 1.35%) containing poly (3, 4-ethylenedioxythiophene) and polystyrene sulfonic acid.

Example 3

First, 49 parts of an aqueous solution of 1% iron (III) sulfate, 64.2 parts of an aqueous 25% sulfuric acid solution, 8.8 parts of 3, 4-ethylenedioxythiophene and 120.7 parts of an aqueous 10.9% peroxodisulfuric acid solution were added to 1859 parts of an aqueous solution containing 22.2 parts of polystyrenesulfonic acid. The pH of the reaction mixture at this point was 0.93. The reaction mixture was stirred at 18 ℃ for 23 hours. Then, 154 parts of cation exchange resin and 232 parts of anion exchange resin were added to the reaction mixture and stirred for 2 hours. Next, the ion exchange resin was filtered off to obtain a deionized aqueous dispersion (2081 parts: solid content 1.35%) containing poly (3, 4-ethylenedioxythiophene) and polystyrene sulfonic acid.

Example 4

First, 49 parts of an aqueous solution of 1% iron (III) sulfate, 30 parts of a concentrated nitric acid solution, 8.8 parts of 3, 4-ethylenedioxythiophene and 121 parts of a 10.9% aqueous solution of peroxodisulfuric acid are added to 1887 parts of an aqueous solution containing 22.2 parts of polystyrenesulfonic acid. The pH of the reaction mixture at this point was 0.83. The reaction mixture was stirred at 18 ℃ for 19 hours. Then, 154 parts of cation exchange resin and 232 parts of anion exchange resin were added to the reaction mixture and stirred for 2 hours. Next, the ion exchange resin was filtered off to obtain a deionized aqueous dispersion (2075 parts: solid content 1.36%) containing poly (3, 4-ethylenedioxythiophene) and polystyrene sulfonic acid.

Example 5

First, 49 parts of an aqueous solution of 1% iron (III) sulfate, 25 parts of trifluoromethanesulfonic acid, 8.8 parts of 3, 4-ethylenedioxythiophene and 121 parts of an aqueous solution of 10.9% peroxodisulfuric acid are added to 1850 parts of an aqueous solution containing 22.2 parts of polystyrenesulfonic acid. The pH of the reaction mixture at this point was 1.22. The reaction mixture was stirred at 18 ℃ for 23 hours. Then, 154 parts of cation exchange resin and 232 parts of anion exchange resin were added to the reaction mixture and stirred for 2 hours. Next, the ion exchange resin was filtered off to obtain a deionized aqueous dispersion (2033 parts: solid content 1.39%) containing poly (3, 4-ethylenedioxythiophene) and polystyrenesulfonic acid.

Example 6

First, 49 parts of an aqueous solution of 1% iron (III) sulfate, 20 parts of a concentrated hydrochloric acid solution, 8.8 parts of 3, 4-ethylenedioxythiophene and 117 parts of an aqueous 10.9% peroxodisulfuric acid solution were added to 1887 parts of an aqueous solution containing 22.2 parts of polystyrenesulfonic acid. The pH of the reaction mixture at this point was 0.95. The reaction mixture was stirred at 18 ℃ for 23 hours. Then, 154 parts of cation exchange resin and 232 parts of anion exchange resin were added to the reaction mixture and stirred for 2 hours. Next, the ion exchange resin was filtered off to obtain a deionized aqueous dispersion (2061 part: solid content 1.37%) containing poly (3, 4-ethylenedioxythiophene) and polystyrenesulfonic acid.

Example 7

First, 5 parts of an aqueous polyester resin dispersion, 4 parts of N-methylformamide and 1 part of a fluorocarbon surfactant were added to 90 parts of an aqueous dispersion containing a complex of poly (3, 4-ethylenedioxythiophene) and polystyrenesulfonic acid obtained in example 1, and the mixture was stirred for one hour, thereby obtaining 100 parts of a coating composition.

Examples 8 to 12

The same operations as in example 7 were carried out except that the aqueous dispersions obtained in example 1 were respectively replaced with the aqueous dispersions obtained in examples 2 to 6, thereby obtaining 100 parts of coating compositions, respectively.

Comparative example 2

The same operations as in example 7 were carried out except that the aqueous dispersion obtained in example 1 was replaced with the aqueous dispersion obtained in comparative example 1, thus obtaining 100 parts of a coating composition.

Example 13

The coating composition obtained in example 7 was coated on the surface of a PET film using three types of wire-drawing bars, respectively, and then dried, so that a substrate coated with a thin film could be obtained. Table 1 shows the evaluation results of the total light transmittance and haze value of the obtained veneered substrate and the surface resistivity and adhesion of the film on the substrate. The total light transmittance and haze values of the PET film used as the substrate were 87.8% and 1.9%.

Examples 14 to 18

The operation was the same as in example 13 except that the coating composition obtained in example 7 was replaced with the coating compositions obtained in examples 8 to 12, respectively. Table 1 collectively lists the results of evaluation of the films obtained on the substrate surfaces.

Comparative example 3

The operation was the same as in example 13 except that the coating composition obtained in example 7 was replaced with the coating composition obtained in comparative example 2. Table 1 collectively lists the results of evaluation of the films obtained on the substrate surfaces.

TABLE 1

	Wire-drawing spindle	Film thickness after drying (μm)	Total light transmittance (%)	Surface resistivity (omega/□)	Haze value (%)	Adhesion (Point)
							Example 13	No.8	0.33	83.3	9.2E+02	2.1	10
No.12	0.49	79.1	5.2E+02	2.3	10
						No.16		0.66	75.1	3.5E+02	2.7	10
Example 14	No.8	0.33	82.2	8.0E+02	2.3								10
						No.12	0.49	77.3	3.8E+02	2.5	10
	No.16	0.66	73.0	2.7E+02	2.6							10
						Example 15	No.8	0.33	82.7	7.1E+02	2.3		10
No.12	0.49	78.0	3.5E+02	2.4	10
							No.16	0.66	74.5	2.6E+02	2.6	10
Example 16	No.8	0.33	81.6	4.5E+02	3.1								10
						No.12	0.49	73.9	2.3E+02	3.7	10
	No.16	0.66	72.1	2.0E+02	3.9							10
						Example 17	No.8	0.33	82.0	5.1E+02	2.8		10
No.12	0.49	74.4	2.7E+02	3.5	10
							No.16	0.66	72.2	2.3E+02	3.7	10
Example 18	No.8	0.33	82.4	4.5E+02	2.7								10
						No.12	0.49	75.3	2.2E+02	3.2	10
	No.16	0.66	73.0	2.0E+02	3.3							10
						Comparative example 3	No.8	0.33	81.1	1.5E+02	2.8		10
No.12	0.49	75.7	7.0E+02	2.2	10
							No.16	0.66	71.4	5.0E+02	2.5	10

As can be seen from table 1, all of the examples exhibited higher total light transmittance and lower surface resistivity than the comparative examples. The haze value and the adhesion of the examples and the comparative examples were substantially equal to each other. Further, the thin film-coated substrates obtained in examples 13 to 18 and comparative example 3 were bent 50 times, each time in the opposite direction, so that the radius of the concave portion of each of the bent films was 1cm, and the surface resistivity before and after the bending was measured. In all cases, there was essentially no change in surface resistivity (within 5%), indicating that they were flexible. FIG. 1 shows the relationship between total light transmittance and surface resistivity for the overlay substrates listed in Table 1. The surface resistivity at 80% total light transmittance is read from the graph, and table 2 lists all the results.

TABLE 2

	Aqueous dispersion of composite	Oxidizing agent	Acid(s)	Surface resistivity at a total light transmittance of 80% (omega/□)
					Example 13	Example 1	Peroxodisulfuric acid	-	600
Example 14	Example 2	Sodium peroxodisulfate	Sulfuric acid	560
					Example 15	Example 3	Peroxodisulfuric acid	Sulfuric acid	470
Example 16	Example 4	Peroxodisulfuric acid	Concentrated nitric acid	390
					Example 17	Example 5	Peroxodisulfuric acid	Trifluoromethanesulfonic acid	420
Example 18	Example 6	Peroxodisulfuric acid	Concentrated hydrochloric acid	350
					Comparative example 3	Comparative example 1	Sodium peroxodisulfate	-	1300

As can be seen from Table 2, in example 13, the composition containing the aqueous dispersion (example 1) (example 7) produced using peroxodisulfuric acid as an oxidizing agent was coated on a substrate, and the surface resistivity (600. omega./□) at a total light transmittance of 80% was lower by 50% or more than that of comparative example 3 using sodium peroxodisulfate.

Also in example 14, the composition (obtained in example 8) containing an aqueous dispersion (obtained in example 2, which corresponds to an aqueous dispersion obtained by adjusting the pH to 0.93 by adding sulfuric acid to comparative example 1) was coated on a substrate, and the surface resistivity at a total light transmittance of 80% was reduced from 1300 Ω/□ (comparative example 3, using the aqueous dispersion of comparative example 1) to 560 Ω/□.

Further, by using peroxodisulfuric acid as an oxidizing agent and further adding an organic acid or an inorganic acid to lower the pH in the same manner as in examples 3 to 6, the surface resistivity at a total light transmittance of 80% was further lowered (see examples 15 to 18).

Thus, by using peroxodisulfuric acid as the oxidizing agent or using an arbitrary oxidizing agent together with an acid for lowering the pH, a coated substrate having good transparency and conductivity can be obtained.

The coating composition containing an aqueous dispersion containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion of the present invention can be easily formed into a film by a wet process, and the film has flexibility and excellent transparency and conductivity. The coating composition of the present invention can be used for producing surface electrodes for electroluminescent displays, pixel electrodes for liquid crystal displays, capacitor electrodes, various transparent electrodes such as transparent electrodes for touch panels, and electromagnetic shields for cathode ray tube displays. In addition, the composition can be formed into a film at a low temperature, and the formed film has flexibility, and thus the film is particularly useful when used as a transparent conductive film formed on a plastic film substrate.

Claims (4)

1. A process for producing an aqueous dispersion containing a complex of poly (3, 4-ethylenedioxythiophene) and a polyanion, which comprises: polymerizing 3, 4-dialkoxythiophene represented by the formula (1):

wherein R is¹And R²Independently is hydrogen or C_1-4Alkyl, or together form a C which may optionally be substituted_1-4Alkylene radical ofThe polymerization is carried out in an aqueous solvent by using peroxodisulfuric acid as an oxidizing agent in the presence of a polyanion, and the polyanion is selected from the group consisting of polycarboxylic acids and polysulfonic acids.

2. The process of claim 1, wherein said polyanion is selected from the group consisting of polyacrylic acid, polymethacrylic acid, polymaleic acid, polystyrene sulfonic acid, and polyvinyl sulfonic acid.

3. A process for producing an aqueous dispersion containing a complex of poly (3, 4-dialkoxythiophene) and a polyanion, which comprises: polymerizing 3, 4-dialkoxythiophene represented by the formula (1):

wherein R is¹And R²Independently is hydrogen or C_1-4Alkyl, or together form a C which may optionally be substituted_1-4Alkylene, wherein the polymerization is carried out in an aqueous solvent by using peroxodisulfuric acid as an oxidizing agent in the presence of a polyanion, wherein an acid selected from the group consisting of water-soluble inorganic acids and water-soluble organic acids is added for lowering the pH of the resulting reaction mixture, and the polyanion is selected from the group consisting of polycarboxylic acids and polysulfonic acids.

4. The process of claim 3, wherein said polyanion is selected from the group consisting of polyacrylic acid, polymethacrylic acid, polymaleic acid, polystyrene sulfonic acid, and polyvinyl sulfonic acid.