JP2001207087A - Method for producing doped electrically conductive polymeric film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a film of a doped electrically conductive polymer. SOLUTION: The method of manufacturing a doped electrically conductive polymeric film comprises coating a solution containing an electrically conductive polymer composed of a repeating unit having a >=4C substituent and a dopant selected from salts capable of oxidizing the polymer at a molar ratio of the dopant to the repeating unit of 2:1 to 1:3 on a substrate, and then, removing the solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a conductive polymer thin film comprising a doped conductive polymer.

[0002]

2. Description of the Related Art As a conductive polymer, a π-conjugated polymer has potential physical properties as a material such as an electronic material, an optical functional material, and a magnetic functional material. Research is being conducted.

[0003] In general, conductive polymers have the characteristic that their electrical conductivity can be greatly increased by doping with an electron donating compound or an electron accepting compound. For example, it is known that polyacetylene exhibits an electric conductivity as high as 10 ⁵ S / cm (Advanc)
ed Materials Vol. 2, P345, 19
1990). However, polyacetylene has a problem that its stability in air is poor. In order to overcome this problem, polypyrrole, polythiophene, and the like containing a nitrogen atom, a sulfur atom, and the like in the main chain skeleton of a π-conjugated polymer have been developed. Polypyrrole or polythiophene itself does not dissolve in various organic solvents, but can be made solvent-soluble by introducing a side chain, for example, an alkyl group having 4 or more carbon atoms, into the main chain skeleton (Japanese Jou).
rnal of Applied Physics. Vo
l. 23, p. 1899, 1984). Among such solvent-soluble conductive polymers, the best studied is poly (3-alkylthiophene) having an alkyl group at the 3-position of the thiophene skeleton. 3-
A polymerization method for imparting regularity to the bond between the alkylthiophene skeletons has been developed (Journal of A).
American Chemical Society V
ol. 114, P10087, 1992, and The
Journal of OrganicChemist
ry Vol. 58, p904, 1993). The conductive polymer obtained by this polymerization method can significantly reduce the number of π-conjugated defects in the main chain, so that the conductivity after doping shows a dramatic increase of 10 ³ S / cm. It has been known.

[0004]

With the exception of very limited examples, such as polyaniline doped with camphorsulfonic acid, conductive polymers that have significantly increased conductivity by doping are generally insoluble in organic solvents. Therefore, in order to form a thin film made of a conductive polymer whose conductivity has been significantly improved by doping, first, a solution of a conductive polymer in a neutral state (undoped state) is applied to a substrate to form the thin film. And
Then, a method of exposing the thin film to a dopant gas or immersing the thin film in a solution of an oxidizable salt to convert the thin film into a doped conductive polymer thin film has been adopted.
The case of poly (3-alkylthiophene) is no exception, and the conductivity of poly (3-alkylthiophene) is significantly improved by adding a solution of a salt capable of oxidizing the solution to the solution of poly (3-alkylthiophene). Attempting to do so renders the solution unstable and often poly (3-alkylthiophene) aggregates in the solution. Also, even if it does not seem to aggregate in a solution, if it is applied to a substrate to form a thin film, it will aggregate on the substrate and a normal thin film will not be formed. Accordingly, an object of the present invention is to provide a method for directly forming a conductive polymer thin film having significantly increased conductivity from a solution of a doped conductive polymer.

[0005]

According to the present invention, a conductive polymer comprising a repeating unit having a substituent having 4 or more carbon atoms and a dopant selected from salts capable of oxidizing the same are provided. A thin film of a doped conductive polymer having significantly increased conductivity by applying a solution having a molar ratio of the dopant to the repeating unit of 2: 1 to 1: 3 to the substrate and removing the solvent. Can be manufactured.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as a conductive polymer, a main chain skeleton is a π-conjugated main chain skeleton, and a substituent having 4 or more carbon atoms is introduced into the main chain skeleton to be soluble in organic solvents. Use a suitable one. As such a conductive polymer, various kinds such as a polypyrrole derivative, a polythiophene derivative, a polyfuran derivative, a polyparaphenylene derivative, and a polyparaphenylenevinylene derivative are known, but a polythiophene derivative is preferably used. As described above, the polythiophene derivative has a structure with regularity in bonding of repeating units, which has very few π conjugate defects in the main chain direction and therefore shows high electric conductivity in a doped state if polymerization conditions are appropriately selected. can do.

The substituent having 4 or more carbon atoms introduced into the conductive polymer is preferably a hydrocarbon group, particularly an alkyl group. The alkyl group may be linear or branched. Among them, hexyl group, heptyl group,
6 carbon atoms such as octyl, nonyl, decyl, etc.
The above is an alkyl group. The repeating unit of the conductive polymer may have a plurality of substituents, in which case at least one substituent may have at least 4 carbon atoms as described above. Therefore, in the case of a polythiophene derivative, its repeating unit can be represented by the following formula (1).

[0008]

Embedded image

(Wherein, R ¹ represents a substituent having 4 or more carbon atoms, and R ² represents a hydrogen atom or a substituent having 1 or more carbon atoms). In the case of a polythiophene derivative, the repeating unit has only one substituent having 4 or more carbon atoms, preferably one alkyl group having 4 or more carbon atoms, particularly 6 or more, and this repeating unit has the following formula (2) It is preferable to use those bonded with regularity as shown in (1).

[0010]

Embedded image

(Wherein, R ¹ represents a substituent having 4 or more carbon atoms, preferably an alkyl group having 4 or more carbon atoms, particularly 6 or more carbon atoms). The solvent for dissolving the conductive polymer is usually chloroform or toluene. , Xylene, tetrahydrofuran and the like are used. As the salt capable of oxidizing the conductive polymer, it is preferable to use a salt having nitrosonium ion, trivalent iron ion or silver ion as a cation. For example, nitrosonium tetrafluoroborate (NOBF ₄ ),
Nitrosonium hexafluorophosphate (NOP
F ₆ ), iron (III) chloride (FeCl ₃ ), silver perchlorate (AgClO ₄ ) and the like are used. As a solvent for dissolving these salts, any solvent that does not cause aggregation or precipitation when mixed with the above-described conductive polymer solution may be used.Examples include acetonitrile, nitrobenzene, benzonitrile, and anisole. . The salt solution is preferably used at a concentration as high as possible.

According to the present invention, there is provided a solution of the above-mentioned conductive polymer,
This is mixed with a solution of a salt capable of oxidizing the solution to prepare a solution containing both the conductive polymer and a salt capable of oxidizing the conductive polymer, and the solution is applied to a substrate to form a thin film. The mixing ratio of the two solutions is such that the molar ratio of the salt to the repeating unit of the conductive polymer is 2: 1 to 1: 3. When the salt molar ratio is less than 2: 1, the conductivity of the resulting thin film does not improve much. Conversely, if the salt molar ratio is greater than 1: 3, the solution becomes unstable and tends to aggregate, making it difficult to form a normal thin film. In order to form a thin film having sufficiently improved conductivity, it is preferable that the mixing molar ratio of the salt to the repeating unit is larger than 4: 3. On the other hand, from the viewpoint of forming a good thin film, the mixing molar ratio of the salt to the repeating unit is preferably smaller than 2: 5. The most preferable range of the mixing molar ratio of the salt to the repeating unit is from 1: 1 to 1: 2 from the viewpoints of both improving the conductivity and forming the thin film. The concentration of the conductive polymer in the solution used for coating is usually 100 mg / ml or less, but is preferably 50 mg / ml or less, particularly preferably 20 mg / ml or less. In general, a lower concentration is less likely to cause aggregation or the like when a conductive polymer solution and a salt solution are mixed, and a good thin film is easily formed.

Any substrate can be used depending on the use of the product. For example, non-conductive objects, such as textiles such as cloth and synthetic resin films, the above solution was applied to glass, etc., and then dried to form a thin film of doped conductive polymer on the surface of these objects. The material can be used as an antistatic material or an electromagnetic wave shielding material. For example, by forming this thin film on the surface of a cathode ray tube for a display, an antistatic cathode ray tube can be obtained. Further, a thin metal plate having a non-conductive oxide film on the surface and a thin film of a conductive polymer doped by the above method formed thereon can be used as a material for a solid electrolytic capacitor. The application method may be appropriately selected from known methods such as a spin coating method, a dipping method, a spray method, and a casting method, depending on the type of the substrate.

[0014]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Example 1 A 1.6 mg / ml chloroform solution of poly (3-octylthiophene) having 98% regularity of repeating units and a nitrosonium tetrafluoroborate concentration of 8
A mg / ml acetonitrile solution was prepared. While stirring the chloroform solution, acetonitrile solution was added thereto,
The solution was slowly dropped until 3-octylthiophene: nitrosonium tetrafluoroborate = 1: 2 (molar ratio). No aggregation of poly (3-octylthiophene) occurred. When the absorption spectrum of this solution was measured, no absorption (peak top: 450 nm) derived from undoped poly (3-octylthiophene) was observed, and poly (3-octylthiophene) substantially doped with high concentration was not observed. (Peak peaks: broad peaks rising from 800 nm and 1200 nm) were observed. Using this solution, a 1.2 μm-thick tetrafluoroborate anion-doped poly (3-octylthiophene) thin film was formed by a casting method. The electrical conductivity of this thin film was measured in air at room temperature by the van der pauw method.
S / cm.

Example 2 In Example 1, the mixing ratio of both solutions was changed to 3-octylthiophene: nitrosonium tetrafluoroborate = 1:
Both solutions were mixed in the same manner as in Example 1, except that the molar ratio was changed to 1. Also in this case, aggregation of poly (3-octylthiophene) did not occur. When the absorption spectrum of this solution was measured, almost no absorption derived from undoped poly (3-octylthiophene) was observed, and substantially high-concentration doped poly (3-octylthiophene) was not observed.
Only the absorptions originating from. Using this solution, a 2.0 μm-thick tetrafluoroborate anion-doped poly (3-octylthiophene) is cast using this solution.
Was prepared. The electrical conductivity of this thin film is 10 S / c
m.

Comparative Example 1 In Example 1, the mixing ratio of both solutions was changed to 3-octylthiophene: nitrosonium tetrafluoroborate =
Both solutions were mixed in the same manner as in Example 1 except that the ratio was 3: 1. Also in this case, aggregation of poly (3-octylthiophene) did not occur. When the absorption spectrum of this solution was measured, the absorption derived from poly (3-octylthiothiophene) in an undoped state and the absorption derived from poly (3-octylthiothiophene) in an undoped state were still strongly observed. . Therefore, even if a thin film is formed with this solution, its electric conductivity is significantly smaller than that of the above embodiment. The absorption derived from the undoped poly (3-octylthiophene) almost disappears after the molar ratio of nitrosonium tetrafluoroborate to 3-octylthiophene becomes larger than 2: 1.

Comparative Example 2 In Example 1, the mixing ratio of both solutions was changed to 3-octylthiophene: nitrosonium tetrafluoroborate = 1:
When both solutions were mixed in the same manner as in Example 1 except that the composition was changed to 4, aggregation of poly (3-octylthiophenyl) occurred, and coating could not be performed to form a thin film.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H01G 9/028 H05K 9/00 X 5E321 H05K 9/00 B29K 81:00 // B29K 81:00 B29L 9:00 B29L 9 : 00 C08L 101: 00 C08L 101: 00 H01G 9/02 331H F term (reference) 4F006 AA11 AA31 AB32 BA07 CA08 4F071 AA01 AA61 AB15 AB19 AB25 AB27 AF37 AH12 BA02 BB02 BC02 4F205 AA34 AB16 AD03 AD04 AD05 AD16 AG73 AH01 GB GB11 GB22 GE24 GF24 4J032 BA04 BB01 BD02 CG01 CG07 4J038 DC001 NA20 5E321 BB23 BB32 BB41 BB44 BB57 GG01 GG05

Claims (12)

[Claims] 1. A conductive polymer comprising a repeating unit having a substituent having 4 or more carbon atoms and a dopant selected from salts capable of oxidizing the same, and the molar ratio of the dopant to the repeating unit is 2 : A method for producing a doped conductive polymer thin film, comprising applying a solution of 1 to 1: 3 to a substrate and removing the solvent. 2. A solution of a conductive polymer comprising a repeating unit having a substituent having 4 or more carbon atoms and a solution of a dopant selected from salts capable of oxidizing the same, comprising: A method for producing a doped conductive polymer thin film, comprising applying a solution prepared by mixing to a ratio of 2: 1 to 1: 3 on a substrate and removing a solvent. 3. The doped conductive polymer thin film according to claim 1, wherein a solution having a molar ratio of the dopant to the repeating unit of 4: 3 to 2: 5 is applied to the substrate. Production method. 4. The doped conductive polymer thin film according to claim 1, wherein the repeating unit of the conductive polymer is represented by the following formula (1). Production method. Embedded image (Wherein, R ¹ represents a substituent having 4 or more carbon atoms, and R ² represents a hydrogen atom or a substituent having 1 or more carbon atoms) 5. The conductive polymer is a polythiophene having a substituent having 4 or more carbon atoms at the 3-position, and the repeating unit has a regular bond represented by the following formula (2): The method for producing a doped conductive polymer thin film according to any one of claims 1 to 4, characterized in that: Embedded image (In the formula, R ¹ represents a substituent having 4 or more carbon atoms.) 6. The method for producing a doped conductive polymer thin film according to claim 5, wherein the substituent having 4 or more carbon atoms represented by R ¹ is an alkyl group having 4 or more carbon atoms. 7. The dope according to claim 1, wherein the dopant is a salt having a cation selected from the group consisting of a nitrosonium ion, a trivalent iron ion and a silver ion. Of producing a conductive polymer thin film. 8. A doped conductive polymer thin film obtained by the method according to claim 1. 9. A composite comprising a substrate and the doped conductive polymer thin film according to claim 8, formed on the surface thereof. 10. An antistatic material comprising a non-conductive substrate and a doped conductive polymer thin film according to claim 8 formed on the surface thereof. 11. An electromagnetic shielding material comprising a non-conductive substrate and the doped conductive polymer thin film according to claim 8 formed on the surface thereof. 12. A material for a solid electrolytic capacitor comprising: a metal sheet having a non-conductive oxide film on the surface; and the doped conductive polymer thin film according to claim 8 formed on the oxide film.