ELECTRICALLY CONDUCTING POLYMER FILM AND METHOD OF MANUFACTURING THE SAME

Abstract: An electrically conducting polymer film comprising an insulating polymer film and an electrically conducting aro­ matic polymer layer formed at least partially in the insulat­ ing polymer film by electrochemical polymerization, where­ in the insulating polymer film comprises a polymer film having at least two laminated layers.

Description: The present invention relates to an electrically conducting polymer film and a method of manufacturing the same. A related invention is disclosed in EP-A-144127, from which the present specification is divided. Conventional electrically conducting polymer films are classified into the following two types: One is a general-purpose polymer material containing carbon black or a metal such as aluminum or stainless steel as a conductive filler. A resultant electrically conducting polymer films have an electrical conductivity of 1 to 10 _13 S.cm _1 (1/Ω.cm) and is used as an antistatic agent, an electromagnetic interference preventing material or the like. This film is prepared such that a polymer is fused and a filler is added thereto, and a resultant material is kneaded and molded. Therefore, a complicated, high-precision process must be used with high reliability of control, resulting in high cost. In addition, it is difficult for this film to obtain an electrical conductivity higher than 1S.cm _1 . In order to achieve a high electrical conductivity, the amount of filler must be increased. These excess amount of filler reduces the mechanical strength of the resultant film. Because of this poor mechanical property, a thin film cannot be easily prepared. The other conventional electrically conducting polymer comprises a polymer material with electrical conductivity. This type of polymer has been developed as a material for various functional elements, polymeric superconductors and molecular device materials which are receiving a great deal of attention these days. For example, the conventional electrically conducting polymer comprises polyacetylene, polyphenylene-sulfide, polyparaphenylene or the like. The main feature of these films lies in the fact that the polymer chains consist of conjugated double bonds, so that carriers are easily mobile along a molecular chain. When a proper impurity is doped, a high electrical conductivity of more than 10 S.cm _1 can be achieved. However, this class of materials is generally unstable in air, and workability of the film is also degraded. In addition to these conventional films, it was reported that some aromatic compounds are electrochemically polymerized in a solution containing an electrolyte, to form an electrically conducting polymer film on an electrode substrate. Aromatic compounds of this type comprise heterocyclic compounds (e.g., pyrrole and thiophene) or polyaromatic compounds such as azulene, pyrene and triphenylene (e.g., J. Bargon, S. Mohmand and R.J. Waltman, IBM Journal of Research & Development, Vol. 27, No. 4, P. 330, 1983). However, a conventional electrically conducting polymer film formed by electrochemical polymerization on the electrode-substrate has the following disadvantages: (1) Since the mechanical strength of the film is weak, the films on the substrate or separated from the substrate are relatively fragile. Moldability of this film becomes poor. (2) Adhesion between film and substrate is weak, so that the film tends to peel from the substrate during film formation or cleaning. (3) The film surface is very coarse, and tends to lose gloss. (4) The resultant film is insoluble and cannot be fused, resulting in poor moldability. (5) When an electrode substrate such as NESA (trade mark) glass which has a high electrical resistance as compared with those of electrolytic solution and resultant polymer film is used, the film thickness becomes non-uniform. (6) Since impurity doping occurs at the same time with the polymerization, it is difficult to control the electrical conductivity of film. (7) Even a film having low electrical conductivity becomes black and has low transmittance of visible light. The resultant film cannot be colored. The principal object of the present invention is to provide an electrically conducting polymer film which has high mechanical strength and can be thin, if needed, and a method of manufacturing the same, wherein electrical conductivity can be controlled in a wide range. It is another object of the present invention to provide an electrically conducting polymer film having high electrical conductivity and a mechanical strength greater than ever before achieved and a method of manufacturing the same even if the film has high electrical conductivity. It is still another object of the present invention to provide an electrically conducting polymer film with excellent workability and a method of manufacturing the same. It is still another object of the present invention to provide an electrically conducting polymer film having a high transmittance of visible light and a method of manufacturing the same. It is still another object of the present invention to provide an electrically conducting polymer film having good adhesion with a substrate and a method of manufacturing the same. In order to achieve the above objects of the present invention, there is provided an electrically conducting polymer film comprising an insulating polymer film and an electrically conducting aromatic polymer layer formed at least partially in the insulating polymer film by diffusion of aromatic monomer into the insulating polymer film and by electrochemical polymerization, wherein the insulating polymer film is a multi-layer composite of different insulating polymers. With the invention the aromatic polymer layer formed at least partially in the insulating polymer film is created by diffusion through the insulating polymer film of monomer corresponding to the aromatic polymer and electrochemical polymerization thereof within the polymer film. In the accompaying drawings: Figure 1 is an illustration of apparatus for performing a method of manufacturing an electrically conducting polymer film according to the present invention; Figures 2A, 2B and 2C are respectively sectional views showing the basic structures of electrically conducting polymer films prepared by the present invention; Figure 3 is a graph showing the relationship between polymerization time and conductivity of a typical electrically conducting polymer film obtained by "the present invention; Figure 4 is a graph showing the relationship between conductivity and transmittance of the typical electrically conducting polymer film obtained by the present invention; Figures 5 and 6 are, respectively, sectional views for explaining steps in manufacturing two- and three-layer electrically conducting polymer films on corresponding electrode substrates by means of electrochemical polymerization according to the present invention; Figure 7 is a sectional view showing an electrically conducting polymer film according to another embodiment of the present invention; Figure 8 shows the steps in manufacturing the polymer film shown in Figure 7; Fig. 9 shows an apparatus for manufacturing an electrically conducting polymer film by using a cylindrical electrode for electrochemical polymerization; Figs. 10 and 11 are, respectively, representations showing plate-like and cylindrical (Fig. 9) electrochemical polymerization electrodes used for manufacturing an electrically conducting polymer film according to the present invention; Fig. 12 is a graph showing the relationship between surface resistance of electrically conducting polymer film and charge density in polymerization according to the present invention; and Figs. 13A and 13B are graphs each showing the relationship between intensity and etching time in Auger Electronic Spectroscopy of the films. An electrically conducting polymer film according to the present invention is manufactured by the principle of the method shown in Fig. 1. Referring to Fig. 1, one of the electrodes dipped in a solution 11 containing an aromatic compound subjected to electrochemical polymerization, a solvent and an electrolyte has a conducting layer 13 such as a conducting metal oxide film serving as an electrode on a substrate 12. An insulating polymer film 14 is formed on the conducting layer 13. The electrode having the construction described above is dipped in the solution 11 together with another(counter) electrode 15. A voltage E is applied between two electrodes. In this case, since the electrode substrate is coated with the insulating polymer film, a current does not flow through the insulating polymer film. As a result, a conducting film will not be formed on the substrate. However, the present inventors have conducted an experiment by using the arrangement described above and found that an electrochemical polymerization occurred even on the insulated electrode surface and that a conducting polymer layer was formed in the insulating polymer film. Many aromatic compounds can be used as monomer in this invention, but pyrrole is mainly used to explain the details of the present invention. Since the polymer films coated on the surface of the electrode are almost insulators, having an electrical conductivity of less than 10 _10 S.cm _1 , polymerization of pyrrole is not considered to occur. However, when a solvent and an electrolyte are properly selected with respect to the insulating polymer film, pyrrole molecules, and electrolyte anions, diffuse in the polymer film and polymerization occurs. The structure of the resultant film varies in accordance with the type of insulating polymer film employed as the base and the composition of a solution subjected to the polymerization reaction. As a result of this process, roughly three types of structures can be obtained, as shown in Figs. 2A, 2B and 2C, respectively. Pyrrole electrochemical polymerization on the electrode covered with the insulating polymer film is initiated on the electrode surface by diffusion, of pyrrole within the film and the electrolyte, so that conducting polypyrrole is produced at an interface between the electrode and film. When the polypyrrole so produced grows within the insulating polymer film, the surface referred to hereinafter as the "electrode side" of the film which is in contact with the electrode becomes conductive. This state is illustrated in Fig. 2A, wherein the opposing surface (referred to hereinafter as the "surface side") of the film is kept insulative. When electrochemical polymerization continues, the conducting portion in the film is increased. Finally, polypyrrole grows to reach the surface, and the film becomes entirely conductive. This state is illustrated in Fig. 2B. Normally, two states shown in Figs. 2A and 2B are obtained. However, when miscibility between the conducting aromatic polymer and the insulating polymer film is poor, or adhesion between the insulating polymer film and the electrode is not sufficient, a conducting polymer layer having a multilayer structure shown in Fig. 2C is formed between the electrode and the polymer film. In this case, the resultant multilayer film often shows a weak adhesion between the insulating polymer film and the conducting polymer layer, and two layers tend to separate from each other. These films cause problems in practice. However, when two or more insulating polymer films are laminated as will be described later, this multilayer structure is effective. The structures adopted in the present invention will be mainly those illustrated in Figs. 2A and 2B. Certain features of the electrically conducting polymer films thus prepared are summarized as follows. However, the characteristics of the films are not limited to these, as will be apparent from the following description. (1) The electrical conductivity can vary from a low conductivity of the insulating material to a high conductivity of about 10² S.cm _1 . The electrical conductivity can change by the polymerization time, as shown in Fig. 3. In this case, electrical conductivity is low at the very beginning of polymerization and is gradually increased, thereby obtaining a film of uniform thickness. (2) Since the electrically conducting polymer film is obtained in the insulating polymer film employed as a base, the resultant conducting polymer film can be thin. In addition, by selecting a suitable insulating polymer film, the resultant film can have high mechanical strength. (3) The present invention can be applied to almost all insulating polymer films. (4) The manufacturing method is simple, and a low-cost electrically conducting polymer film can be obtained. (5) When an insulating polymer film having high adhesion with the electrode surface is used, or a noble metal substrate is used as electrode, an electrically conducting polymer film having good adhesion with the substrate can be obtained. (6) Even if a transparent electrode such as NESA glass or indium tin oxide (ITO) having a relatively high surface resistance is used, polymerization can be performed uniformly, thereby obtaining a film having uniform electrical conductivity. (7) Although a conventional electrically conducting polymer has a color close to black, a film having a high transmittance can be obtained by adjusting the electrochemical polymerization time according to the present invention. Fig. 4 shows the relationship between optical density and conductivity of polypyrrole polyvinylcarbazole composite film prepared by this invention. Typical examples of the various materials used in the present invention will be described hereinafter. An insulating polymer film used in the present invention may comprise a thermoplastic resin: polystyrene; a polystyrene derivative such as chloromethylated polystyrene and polychlorostyrene; a copolymer of styrene and a monomer (e.g., various vinyl esters, vinyl ethers, acrylic acids and their esters, metacrylic acids and their esters, maleic acid and its esters, fumaric acid and its esters, maleic anhydride, halogenovinylidene compounds, vinylchloride acrylonitrile, methacrylonitrile and propylene); or a copolymer of styrene with any aromatic vinyl polymer such as polyvinyl carbazole. Furthermore, the insulating polymer film may comprise a polyvinylchloride resin (i.e., polyvinyl chloride and a copolymer of vinyl chloride with a monomer described above). The insulating polymer film may also comprise a copolymer of vinylidene chloride and one of various vinyl esters, vinyl ethers, acrylonitrile, methacrylonitrile and vinylchloride; polyvinylidene fluoride or a copolymer of vinylidene fluoride with monomer described above, or polyvinyl acetate or copolymer of vinyl acetate with monomer described above. The insulating polymer film may comprise polyethylene, a copolymer of ethylene with a monomer as described above, polyethylene telephthalate, any nylon, polycarbonate, any cellulose, polyvinyl alcohol, rubber or the like. The insulating polymer film may also comprise a thermosetting resin such as epoxy resin, phenol resin, melamine resin, urea resin, acetal resin, polyimide resin, RTV silicone resin. The insulating polymer film may comprise a polymer film obtained by plasma polymerization. Additives such as a plasticizer, a pigment, a plastid, a conductive filler, a defogging agent and a rust inhibitor may be used. In this case, it is desired to use the additives which dissolve very sparingly in the electrolytic solution. An aromatic compound subjected to electrochemical polymerization can be selected from pyrrole, 3-methylpyrrole, N-methylpyrrole, N-phenylpyrrole, thiophene, 3-methylthiophene, aniline, furan, phenol, thiophenol, selenophene, tellurophene, biphenyl, azulene, p-terphenyl, o-terphenyl, 2-hydroxybiphenyl, diphenylsulfide, 2-(α-thienyl)thiophene, 2-(α-thienyl)furan, 2-(2-pyrrolyl)pyrrole, 2-(2-pyrrolyl)thiophene, 2-phenylthiophene, α-thienylphenyl ether, β-furanyl-α-thienylselenide, 2-(2-pyrrolyl)selenophene, 2-(2-seleninyl)tellurophene, N-vinylcarbazole, N-ethynylcarbazole, methylazulene and pyrene. An electrically conducting polymer solution must have a proper composition adjusted for the type of insulating polymer film used. The solution must satisfy at least the following conditions: (1) The solution does not dissolve the insulating polymer film. (2) The solution dissolves an aromatic compound which can be electrochemically polymerized with the electrolyte. (3) The solution has an affinity with the insulating polymer so that an aromatic compound which can be subjected to electrochemical polymerization can be diffused in the insulating polymer film. An electrolyte for electrochemical polymerization comprises any compound such as organic quaternary ammonium salts, inorganic salts, or strong acids of protone acid. An acetonitrile solvent is normally used. However, any solvent can be used when the solvent allows the aromatic compound to perform electrochemical polymerization and dissolves a proper electrolyte. For example, the solvent is selected from a nitrobenzene-based solvent, a propylene carbonate-based solvent, an ethylene glycol-based solvent, an aqueous solvent, an N,N-dimethylformamide-based solvent, and a dimethylsulfoxide-based solvent. However, any other solvent may, if necessary, be used. An electrochemical polymerization substrate comprises a noble metal such as gold, platinum and palladium; a base metal (that is, a metal of lower worth and greater reactivity than a noble metal) such as nickel, chromium and stainless steel; a conducting metal oxide such as, stannic oxide, indium oxide and ITO (indium tin oxide); an inorganic semiconductor such as silicon and amorphous silicon; or a material obtained by depositing one of the above materials on a proper substrate, by means of evaporation, sputtering, CVD, plating, or coating. The electrochemical polymerization substrate may comprise a laminate obtained by stacking at least two layers of the above-mentioned electrode materials. An electrode laminate may be formed into a drum to produce films continuously. The resultant electrically conducting polymer film can be used as an electromagnetic interference preventing film, an antistatic film, a photosensitive image sensor film, a solar battery film, and so on. In addition, and in accordance with the present invention, the present inventors found that at least two different insulating films can be layered in the electrochemical polymerization, and that a resultant layered film had often superior film quality to that of a single conducting film. As shown in Fig. 5, a first insulating polymer film 14 is coated on a substrate 12 having an electrode 13. A second insulating polymer film 21 is formed on the first insulating polymer film 14 in a state (a). The electrochemical polymerization of aromatic compounds by using this electrode produces a two-layer composite electrically conducting polymer film.., In this case, the aromatic polymer is mixed in the two layers 14 and 21 as shown in state (b), or is mixed only in the layer 14 as shown in state (c). Even an insulating polymer film having at least three layers can be a composite electrically conducting polymer film having a multi-layer structure by properly selecting the type and thickness of the polymer film and the type of solvent. When a polymer compound containing an epoxy group such as polyglycidyl methacrylate, or a polymer compound containing an OH group such as novolak resin is used as the insulating polymer film, a resultant conducting film is strongly adhered to the electrode surface. On the other hand, when an aromatic polymer such as polystyrene, chloromethylated polystyrene, polyvinylphthalate, or polyvinylcarbazole is used to form the insulating polymer film, a relatively uniform composite electrically conducting polymer film having a controlled electrical conductivity is obtained. However, this polymer film has weak adhesion to the substrate and can be easily peeled therefrom. When an aromatic polymer layer is laminated on a polymer layer having good adhesion with electrode surface, the electrochemical polymerization produces a uniform composite electrically conducting film which has good adhesion and uniform and controllable conductivity. When a polymer film, which has poor miscibility with electrically polymerized conductive polymer, such as polyethylene or polypropylene type polymer is used as top layer of two-layer insulating film, a two-layer structure having a composite layer of conductive polymer with bottom insulating film and top polymer film which is still insulated can be easily obtained. This insulating film can be used as protective layer of electrically conducting film. In the case of combination of an aromatic polymer film as bottom layer and a polymer film with poor miscibility as top layer the electrochemical polymerization produces uniform, conductivity-controlled composite electrically conducting polymer covered with an insulating polymer film. When three kinds of polymer film are laminated, a multilayer composite conducting polymer film having a combination of respective layers can be obtained. As shown in Fig. 6, a polymer film (first layer) 14 having good adhesion with a substrate 12 is formed on the substrate 12 having a conductive surface (an electrode) 13 thereon. An aromatic polymer film (second layer) 21 for controlling electrical conductivity is formed on the first layer 14. A polymer film (third layer) 23 with poor miscibility is formed on the second layer 21. The resultant substrate (a) is electrochemically polymerized to obtain a form, conductivity-controlled composite electrically conducting polymer film having good adhesion, which are covered with insulating polymer film. According to the conducting polymer film of the present invention, the transparency of film is improved, as previously described. The present inventors found that when the insulating polymer film was made conductive and the electrochemical polymerization time was shortened, the electrical conductivity could not be greatly increased, but the resultant semiconducting film had high transmittance to visible light: However, when a film has a practical thickness such as, more than 20 µm (micron),short polyrization time cannot make the whole film conductive and only the film surface which is in contact with the electrode surface becomes conductive. When the resultant film is used as a semiconductor film having a high transmittance to visible light, only one conductive surface is utilized. On the other hand, when both surfaces of the film having the thickness described above are made conductive, the electrochemical polymerization time must be prolonged, thereby decreasing the transmittance. According to the present invention, a conducting polymer film with electrochemical polymers mixed in the surface and electrode side layers of the film can be provided although the entire film is not made conductive. Fig. 7 shows a typical example of the above case. Referring to Fig. 7, upper and lower surface layers 32 and 33 of an insulating polymer film 31 comprise a composite structure obtained by electrochemically polymerizing the aromatic compound in the polymer film. The thickness of the composite conducting surface layer greatly depends on the electrochemical polymerization conditions of the aromatic compound, especially the electrochemical polymerization time. When the polymerization time is increased, the thickness of the conductive composite layer is increased. As a result, the entire film is made conductive, and no insulating part will appear. Fig 8 shows steps of a method of manufacturing a conducting polymer film according to the present invention. Reference numerals 31 to 33 in Fig. 8 denote the same parts in Fig. 7. Reference numerals 30 and 30′ denote electrodes. An insulating polymer film 31 is adhered to an electrode 30 (step A). The electrode 30 is used as a positive electrode, and electrochemical polymerization of an aromatic compound is performed in an electrochemical polymerization solution. An electrochemical polymer is formed in a surface layer 32 of the polymer film which is in contact with the electrode 30 (step B). The resultant film is peeled from the electrode, and the opposite surface is adhered to the electrode 30′ (step C). This electrode is used as the positive electrode, and electrochemical polymerization of an aromatic compound is performed in the electrochemical polymerization solution. A composite electrochemical polymer is formed in the surface layer 33 adhered to the surface thereof which is in contact with the electrode 30′ (step D). A conducting polymer film having upper and lower conducting layers is the result (E). In the above process, the electrodes 30 and 30' may be the same or different in respective steps. In addition, the electrochemical polymerization solution used in step B may be the same as or different from that in step D. In other words, electrochemical polymers of different types of aromatic compounds may be used. In order to manufacture an electrically conducting polymer film according to the present invention, a continuous manufacturing apparatus using a cylindrical electrode can be used to improve productivity and decrease manufacturing cost. Fig. 9 is a side view of a conducting film forming apparatus using the cylindrical electrode for electrochemical polymerization. Referring to Fig. 9, reference numeral 81 denotes a cylindrical electrode; 82, a film; 83, a thermal transfer roller; 84, an electrochemical polymerization solution; 85, an electrochemical polymerization tank; 86, a counter electrode; 87, a terminal; 88, a guide collec; and 89, a power source. An insulating polymer film is adhered by the thermal transfer roller 83 to the cylindrical electrode 81. The thermal transfer roller 83 is slowly rotated to dip the film in the electrolytic solution. A voltage is applied between the counter electrode 86 and the terminal 87 so as to perform electrochemical polymerization. Polymerization continues for a time period during which the film is being dipped in the solution. The polymerized film is peeled from the cylindrical electrode and washed and dried. The dried film is then wound. Instead of adhering the film by the thermal transfer roller, the film can be directly formed by casting on the roller, thereby continuously forming the conducting film. In addition, an electrode material is proposed according to the present invention which allows formation of a conducting polymer film of large area. When electrochemical polymerization is performed, the polymer film must be adhered to the electrode and must be easilypeeled from the electrode so as to obtain a uniform conducting film of large area when polymerization is completed. However, when a noble metal substrate as previously mentioned is used, the substrate has uniformity but is expensive. In addition, it is often difficult to peel the film from the substrate. When a base metal is used, it has uniformity but the film cannot easily be peeled off. When electrochemical polymerization reaction is repeatedly performed, the surface of the base metal electrode is often degraded by a side reaction. When a metal oxide such as ITO is used, it has a higher resistance than that of a metal substrate. As a result, a slight resistance distribution of the conducting film occurs. In order to overcome these problems, a conducting metal oxide layer or a doped semiconductor layer is laminated on the base metal layer so as to constitute the most suitable electrode. Fig. 10 shows a laminate obtained such that a base metal layer 42 is formed on an insulating substrate 41, and such that an electrically conducting metal oxide layer or a doped inorganic semiconductor layer 43 is formed. The base metal layer comprises aluminum, chromium, nickel, stainless steel or copper and is formed by evaporation, sputtering or the like. The thickness of the base metal layer may slightly vary in accordance with electrical conductivity, but must be more than 50 nm (500 A°) so as to obtain a uniform electrically conducting electrochemical polymer. The electrically conducting metal oxide layer or doped inorganic semiconductor layer is laminated on this base metal layer. The conducting metal oxide comprising tin oxide, indium oxide, indium tin oxide (ITO) or the like is normally formed by evaporation or sputtering. An inorganic semiconductor may be used as a laminate layer in addition to the metal oxide. In this case, a substantial amount of impurity is doped in a semiconductor layer so as to effectively decrease electrical resistance. Amorphous or polysilicon is the best material for such a uniform semiconductor layer without pinholes. However, germanium or gallium arsenide may be used in place of amorphous silicon. The laminate is formed by CVD, sputtering or the like. An impurity is doped in a corresponding semiconductor material. Fig. 11 shows a cylindrical electrode for continuously forming an electrically conducting polymer film. In order to continuously form a conducting film by electrochemical polymerization, it is preferable to form an electrode in a drum-like shape. Referring to Fig. 11, when an electrically conducting metal oxide layer or a doped inorganic semiconductor layer 53 is formed on a base metal drum 51, a base metal layer 52 is formed on the surface of a drum made of any material, and the electrically conducting metal oxide layer or the doped inorganic semiconductor layer 53 is laminated on the base metal layer 52. A film is formed on the drum-like electrode, and electrochemical polymerization is performed in the electrochemical polymerization tank while the drum is being rotated. The resultant conducting polymer film is peeled from the drum and washed. Thus, a uniform film can be continuously formed, and repeated use of the electrode can be obtained. In order to make the diffusion of aromatic compound to be polymerized and electrolyte anion in the insulating polymer film much easier, the film may comprise a porous material. In this porous film the electrolyte and the aromatic compound tend to be diffused, and polymerization is accelerated, thereby obtaining a uniform conducting film for a shorter polymerization time. A method of preparing a porous polymer film is known wherein a gel of a polymer solution is prepared and a solvent or the like is removed or any foaming agent is used. A porous material prepared by a solvent extraction method or neutron radiation method is commercially available. Such a porous material can be used as a film which will be made conductive according to the present invention. However, in this case, a porous film must be adhered to the electrode. For this reason, various methods may be proposed. Utilizing a simplest method, a porous film is adhered to the electrode through a thin phenol or epoxy adhesive layer. In this case, the phenol or epoxy resin layer is also made conductive. According to the present invention, when thickness of an electrically conducting film is small, it is uniform and has high electrical conductivity. However, when thickness is increased, the film becomes nonuniform. In order to solve this problem, a conductivity filler may be used. Examples of the filler may include: a carbon material such as carbon powder, carbon fiber and acetylene black; powder or flake of a metal such as aluminum, copper and stainless steel; a powder or flake of a conducting metal compound such as indium oxide and titanium oxide; a powder or flake of a noble metal such as gold, platinum, rhodium and palladium; and a powder or flake of a base metal such as nickel, stainless steel, and brass. However, a metal such as aluminum and copper is partially subjected to a side reaction when electrochemical polymerization of an aromatic compound is performed. Therefore, these metals are not preferred. When thickness is increased or miscibility between the insulating polymer film and the aromatic polymer material obtained by electrochemical polymerization is poor, a uniform conducting film cannot be formed. In order to improve this, a removable material is premixed in a polymer film when the polymer film is coated on the electrode substrate. This material is removed before and during the reaction, and a number of small voids are formed in the polymer film. For this reason, the electrolyte and the aromatic compound tend to be diffused in the film, and polymerization is accelerated. As a result, a uniform electrically conducting polymer film is prepared. The removable material is preferably mixed with the polymer film for the above reason so as to form a uniform film. The removable material may comprise a material (e.g., low-melting point halogenated hydrocarbon, phthalic anhydride and camphor) which is volatile by heat and/or reduced pressure; a material (e.g., an aromatic compound as a raw material for pyrrole, an electrolyte, or an electrolyte-soluble material such as dialkylphthalate) soluble in an electrochemical polymerization solution; or a combination of the solvent-soluble material and a solvent (i.e., a combination of sodium chloride and water). The removable material is then removed before and during the reaction. The present invention will now be described by way of examples. However, the present invention will not be limited to these examples. Examples 1 Chloromethylated polystyrene (to be referred to as a CMS hereinafter; molecular weight: 300,000) was coated on a NESA glass substrate to a thickness of 1.5 µm. Light from a 500-W Xe lamp irradiated the film to crosslink the CMS film. A cyclohexane-chlorobenzene (2: 1) mixture of ethylene-vinylacetate (88: 12) copolymer was spin-coated on the film to form a film having a thickness of 1.0 µm. The resultant substrate was dipped together with a platinum mesh electrode as the counter electrode in an acetonitrile-tetrahydrofuran-chlorobenzene (80: 10 : 10) solvent mixture added with 1 mol/ℓ of pyrrole and 0.3 mol/ℓ of tetraammonium tetrafluoroborate as an electrolyte. On the substrate, pyrrole was electrochemically polymerized at a voltage of 2.0 V for 20 minutes to precipitate black polypyrrole on the substrate. The resultant film had a thickness of 2.9 µm and could be easily peeled from the NESA glass substrate. The film structure had a two-layer structure wherein a black conducting film obtained by mixing CMS and polypyrrole and an EVA film were laminated. The EVA film had high mechanical strength, so that the resultant two-layer structure also had high mechanical strength. An electrical conductivity of the composite CMS-polypyrrole film was 4.3 S.cm _1 , and the EVA film was insulative and had an electrical conductivity less than 10 _7 S.cm _1 . In the two-layer film, since crosslinked CMS was slightly swelled in the casting EVA solvent, CMS and EVA were slightly mixed at an interface thereof. As a result, adhesion between these two layers was good, nor would the layers peel from each other at their interface. Example 2 Five NESA glass substrates each coated with two films consisting of a CMS film (thickness of 1.5 µm and an EVA film (thickness of 1.2 µm) in the same manner as in Example 1 were prepared. These substrates were dipped in the same electrochemical polymerization solution as in Example 1 and pyrrole was electrochemically polymerized at a voltage of 2.0 V for 10 seconds, 30 seconds, 2 minutes, 10 minutes and 60 minutes, respectively. When the polymerization time was increased, the film thickness was increased. The respective substrates were covered with uniform, smooth EVA films. Each resultant film comprised a composite CMS-polypyrrole film and was peeled from the corresponding substrate. The electrical conductivities of the CMS-polypyrrole surfaces of the respective composite films were 2 × 10 _4 , 4 × 10 _2 , 1 × 10 _1 , 3.2 × 10 _1 and 9.2 S.cm _1 . The electrical conductivities of these films were found to be controlled in accordance with the polymerization time. Example 3 Polyglycidyl methacrylate (to be referred to as PGMA hereinafter; molecular weight: 85,000) was coated to a thickness of 0.2 µm on an n-type silicon substrate having a resistivity of 5 S.cm _1 . The PGMA film was baked at a temperature of 200°C for 30 minutes. Polyvinyl carbazole (to be referred to as PVCZ hereinafter; molecular weight: 460,000) was coated on the PGMA film to a thickness of 1.0 µm. The resultant substrate was used as a positive electrode and was dipped together with a platinum mesh electrode as a counter electrode in an acetonitrile solution dissolved with 1 mol/ℓ of thiophene and 0.2 mol/ℓ of tetraethylammonium perchlorate. On the substrate thiophene was electrochemically polymerized in a nitrogen gas atmosphere at a voltage of 3.0 V for 20 minutes, thereby precipitating bluish black polythiophene on the substrate. This film had a substantially uniform thickness of 1.5 µm and had good adhesion with the substrate. The film was cut from the substrate and subjected to measurement of electrical conductivity from the surface thereof. An electrical conductivity was 0.75 S.cm _1 . Polythiophene was hybridized in two layers of the PGMA and PVCZ layers. Example 4 In the same manner as in Example 3, PGMA and PVCZ were coated on an n-type silicon substrate to thicknesses of 0.8 µm and 0.2 µm respectively. EVA was then coated to a surface of the PVCZ layer to a thickness of 1.2 µm. The resultant substrate was dipped together with a platinum mesh electrode as a counter electrode in an acetonitrile-tetrahydrofuran-chlorobenzene (9: 1: 1) solvent containing 1 mol/ℓ of pyrrole and O.4 mol/ℓ of tetraethylammonium perchlorate. On the substrate pyrrole was electrochemically polymerized at a voltage of 2.0 V for 35 minutes. Polypyrrole was precipitated on the substrate and the composite film had a thickness of 2.6 µm. The resultant film had good., adhesion with the substrate. The surface of the film was glossy in the same manner as in the state before electrochemical polymerization was performed. The film was cut off from the substrate, and the structure and electrical conductivity of the film were examined. The EVA layer was laminated on a composite PGMA/PVCZ layer mixed with polypyrrole. The PGMA/PVCZ surface and the EVA surface had electrical conductivities of 16 S.cm _1 and 2 × 10 _8 S.cm _1 , respectively. When the laminate film formed on this substrate and the film without the EVA film of Example 2 were exposed to air for 30 days, electrical conductivity of the film in Example 2 was decreased by 10%, while the film conductivity of Example 106 was decreased by only 2%. This indicated that the EVA film served as a protective film, and that the stability of the electrically conducting polymer could be improved by the laminate structure. Example 5 Novolak resin (molecular weight of 8,000) was coated on a MESA glass substrate to a thickness of 0.2 µm and was baked at a temperature of 200°C for 30 minutes. Poly-2-vinylnaphthalene (molecular weight of 18,000) was coated on the novolak resin film to a thickness of 1.1 µm. The resultant substrate was dipped in an acetonitrile-water-ethylene glycol (98: 1: 1) solution added with 1 mol/ℓ of 3-methylpyrrole and 0.4 mol/ℓ of tetraethylammonium p-toluenesulfonale. On the substrate 3-methylpyrrole was electrochemically polymerized at a voltage of 1.4 V for 20 minutes to precipitate bluish black poly-3-methylpyrrole. The resultant film had good adhesion with the substrate and was entirely mixed with conducting poly-3-methylpyrrole. The film was peeled from the substrate, and its electrical conductivity was 0.5 S.cm _1 . Example 6 Chromium and indium tin oxide (ITO) were deposited on a glass substrate to thicknesses of 10 nm and 50 nm, thereby constituting an electrochemical polymerization electrode substrate. A methylisobutylketone solution of polyglycidyl methacrylate was spin-coated on the electrode substrate to form a polyglycidyl methacrylate film having a thickness of 2 µm. A porous polycarbonate film NUCLEPORE (trade name) available from NUCLEPORE Corp. and having a thickness of 1 mm was bonded by thermocompression on the polyglycidyl methacrylate film. The resultant substrate was heated in a nitrogen atmosphere at a temperature of 150°C for 30 minutes. On the other hand, an acetonitrile solution containing 1 mol/ℓ of thiophene and 0.4 mol/ℓ of tetraethylammonium perchlorate was prepared as an electrochemical polymerization solution. The electrode substrate with the film was dipped together with a platinum mesh electrode as a counter electrode in this solution. A voltage of 4.0 V was applied between these two electrodes to form polythiophene. The resultant film was peeled from the substrate, and its electrical conductivity was measured. An electrical conductivity along the direction of thickness of the film was 0.8 S.cm _1 , an electrode side thereof was 0.4 S.cm _1 , and a surface side thereof was, 0.25 S.cm _1 . A substantially uniform electrically conducting polymer film was obtained. Example 7 A methyl ethyl ketone solution was prepared by mixing polystyrene resin and tin oxide powder having a particle size of 0.2 to 0.5 µm at a volume ratio of 3: 1. The solution was coated by a doctor blade on the same electrode as in Example 6 to form a tin oxide-containing polystyrene film having a thickness of 80 µm. This film was dried in an oven at a temperature of 100°C for 15 minutes. On the other hand, an acetonitrile-methyl ethyl ketone containing 1.2 mols/ℓ of thiophene and 0.4 mol/ℓ of tetrabutylammonium p-toluenesulfonate (2: 1) was prepared as an electrochemical polymerization solution. The electrode with the film was dipped in this solution for 15 minutes. A voltage of 4.0 V was applied between the electrode with the film and a platinum-plated titanium mesh electrode as a counter electrode for 20 minutes to electrochemically polymerize thiophene. The resultant film was obtained such that tin oxide and polythiophene were dispersed in polystyrene and the film could be easily peeled from the electrode. An electrical conductivity of the film before polymerization was 2 × 10 _5 S.cm _1 . However, after polymerization the electrical conductivity was increased to 3-2 S.cm _1 . In addition, the mechanical strength of the film was also improved.

Claims: 1. An electrically conducting polymer film comprising an insulating polymer film and an electrically conducting aromatic polymer layer formed at least partially in the insulating polymer film by diffusion of aromatic monomer into the insulating polymer film and by electrochemical polymerization, wherein the insulating polymer film is a multi-layer composite of different insulating polymers. 2. A film according to Claim 1, wherein the insulating polymer film comprises a cross-linked polymer material. 3. A film according to either of the preceding claims wherein the conducting aromatic polymer layer is formed on each of two surfaces of the insulating polymer film. 4. A film as claimed in any one of claims 1 to 3, wherein the insulating polymer film comprises a thermoplastic resin. 5. A film as claimed in any one of claims 1 to 4, wherein the insulating polymer film is porous. 6. A film as claimed in any one of the preceding claims wherein the insulating polymer film contains a conductive filler. 7. A method of manufacturing an electrically conducting polymer film comprising the step of: forming an insulating polymer film on an electrode substrate; selecting an electrochemical polymerization solution containing aromatic monomer capable of diffusing into the insulating polymer film; and forming an electrically conducting aromatic polymer layer in at least part of the insulating polymer film by diffusion of aromatic monomer into the insulating polymer film and by electrochemical polymerization of said monomer, using as cathode an electrode on the electrode substrate, and as anode a counter electrode, both electrodes being dipped in the electrochemical polymerization solution as electrolyte, and a voltage being applied between the two electrodes to drive said electrochemical polymerization, and wherein the insulating polymer film is a multi-layer composite of different insulating polymers. 8. A method according to Claim 7, wherein the insulating polymer film comprises a cross-linked polymer material, and the step of forming the conducting aromatic polymer layer includes the step of cross-linking the insulating polymer film. 9. A method according to Claim 7 or 8, wherein the insulating polymer film comprises a thermoplastic resin. 10. A method according to any one of Claims 7, 8 or 9, wherein the insulating polymer film is porous. 11. A method according to any one of Claims 7 to 10, wherein the insulating polymer film contains a conductive filler. 12. A method according to any one of Claims 7 to 11, wherein the insulating polymer film 'is formed on an electrode substrate. 13. A method according to any one of Claims 7 to 12, wherein the conducting aromatic polymer layer is formed on each of two surfaces of the insulating polymer film. 14. A method according to any one of Claims 7 to 13, wherein the step of forming the conducting aromatic polymer layer includes: adhering an insulating polymer to a positive electrode substrate; by electrochemical polymerization forming a first conductive aromatic polymer layer at the surface of the insulating polymer film which contacts the substrate; peeling the polymer film from the electrode substrate; bringing into contact with the electrode substrate that surface of the polymer film which is opposite to the surface which carries the first conducting aromatic layer; and forming a second conducting aromatic polymer compound layer at the surface in contact with the electrode substrate by electrochemical polymerization. 15. A method according to any one of Claims 7 to 14, wherein the step of forming the insulating polymer film on the electrode substrate includes the step of adding a removable material in the insulating polymer film, and the step of forming the conducting aromatic polymer layer includes the step of removing the removable material before and/or during electrochemical polymerization. 16. A method according to Claim 15, wherein the step of removing the removable material comprises a heat treatment. 17. A method according to Claim 15 or 16, wherein the step of removing the removable material comprises a reduced pressure treatment. 18. A method according to any one of Claims 15 to 17, wherein the removable material is a material which is soluble in an electrochemical polymerization solution. 19. A method according to any one of Claims 15 to 17, wherein the removable material comprises a material which is soluble in a solvent. 20. A method according to any one of Claims 7 to 19, wherein the step of forming the insulating polymer film on the electrode substrate includes the step of coating an adhesive on the electrode substrate and the step of thermocompressively bonding the insulating polymer film to the adhesive.

Inventors: NIWA, OSAMU, TAMAMURA, TOSHIAKI
Applicants: NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Application year: 1984
Main classification: H01B1
IPC codes: H01B1, H01M4, C08G61