POLYMER FILM WITH CONDUCTIVE PATTERN AND METHOD OF MANUFACTURING THE SAME

Abstract: A polymer film with a conductive electrode has an in­ sulated polymer film (7) with an electrically conductive pat­ tern (6) containing an electrically conductive polymer of an aromatic compound, the conductive pattern being formed on at least one major surface of the insulated film, and having an internal portion extending into the film from said surface.

Description: The present invention relates to a polymer film with a conductive pattern and a method of manufacturing the same. There is increasing demand for digital display devices (e.g., liquid crystal display devices), touch-pen type manual input devices and facsimile systems. Polymer films with conductive patterns at low cost are needed for connectors (e.g., for electrode connections in terminal blocks of liquid crystal display devices and electrochromic display devices, input connections for touch pens, output connections of image sensors in facsimile machines) of input/output devices, and this requires simple pattern formation. As the polymer films with conductive patterns used for the above purposes there have been proposed films obtained by mixing an electrically conductive filler in a suitable thermoplastic resin and films obtained by depositing, spraying or plating an electrically conductive material on a suitable polymer film. It is easy to obtain uniform conductivity in these conventional films. However, in order to obtain a polymer film with a conductive pattern, a suitable patterning process is required. It is therefore, a principal object of the present invention to provide an improved polymer film with a conductive pattern, and a method of manufacturing the same. EP-A-0140304 discloses a method for producing electrically-conductive paths in crystalline poly (arylene sulphide) by subjecting areas of the polymer pattern-wise to heat or solvent treatment to render it amorphous in those areas, and then relying upon the differential receptivity of the amorphous material to dopants in solution, to render the amorphous areas conductive by a doping treatment. According to a first aspect of the present invention, there is provided a polymer film containing a conductive pattern characterized in that it comprises a film of an insulating polymer which includes pattern areas defined by the presence of an electrically conductive polymer of an aromatic compound, rendered electrically conductive by in situ polymerization, and non-pattern areas defined by the absence of the said conductive polymer, the conductive pattern having an internal portion extending into the thickness of the film from at least one major surface of said film. According to another aspect of the present invention, there is provided a method of manufacturing an insulating polymer film which has an electrically conductive pattern therein characterized by the steps of:- i) establishing the polymer film on a major surface of an electrode housing electrically conductive portions; ii) causing an electrolyte solution and an aromatic compound to diffuse within the polymer film through to the said major surface; iii) electrochemically polymerizing the aromatic compound pattern-wise at the major surface to form the said electrically conductive pattern in the polymer film at portions which contact said electrically conductive portions of the electrode; iv) continuing the electrochemical polymerization step to cause the interface between the conductive pattern and the insulating polymer material to advance through the thickness of the polymer film, away from the said major surface. For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figs. 1A to 1D are respectively sectional views illustrating particular steps in manufacturing a polymer film with a conductive pattern according to the present invention; Fig. 2 is a sectional view showing a polymer film with a conductive pattern according to another embodiment of the present invention; Figs. 3A to 3C are respectively sectional views which illustrate particular steps in manufacturing a polymer film with a conductive pattern according to still another embodiment of the present invention; Figs. 4 and 5 are sectional views showing polymer films with conductive patterns according to other embodiments of the present invention, respectively; Figs. 6A to 6F are respectively sectional views which illustrate particular steps in creating the pattern of Fig.5; Figs. 7A to 7D are respectively sectional views illustrating particular steps in manufacturing a polymer film with a conductive pattern according to still another embodiment of the present invention; and Fig. 8 is a plan view of the polymer film with the conductive pattern prepared by the steps in Fig. 1. Figs. 1A to 1D show a polymer film with a conductive pattern of the present invention and the principle of the method of manufacturing the same. Referring to Figs 1A to 1D, reference numeral 1 denotes an insulating substrate; 3, an electrically conductive layer formed on the entire surface of the insulating substrate 1; 4, an insulating pattern; 5, a polymer film; 6, an electrically conductive portion; and 7, an insulating portion. Figs. 3A to 3C are respectively sectional views for explaining the steps in manufacturing a polymer film with a conductive pattern according to still another embodiment of the present invention; Figs. 4 and 5 are sectional views showing polymer films with conductive patterns according to other embodiments of the present invention, respectively; Figs. 6A to 6F are respectively sectional views for explaining the steps in manufacturing the pattern of Fig. 5; Figs. 7A to 7D are respectively sectional views for explaining the steps in manufacturing a polymer film with a conductive pattern according to still another embodiment of the present invention; and Fig. 8 is a plan view of the polymer film with the conductive pattern prepared by the steps in Fig. 1. Figs. 1A to 1D show a polymer film with a conductive pattern of the present invention and the principle of the method of manufacturing the same. Referring to Figs. 1A to 1D, reference numeral 1 denotes an insulating substrate; 3, an electrically conductive layer formed on the entire surface of the insulating substrate 1; 4, an insulating pattern; 5, a polymer film; 6, an electrically conductive portion; and 7, an insulating portion. As shown in Fig. 1A, the electrically conductive layer 3 is formed on the insulating substrate 1. The insulating layer 4 with a desired pattern is formed by lithography on the electrically conductive layer 3. The insulating substrate 1, the electrically conductive layer 3 and the insulating pattern 4 constitute an electrode substrate 10. In this case, the electrically conductive layer comprises a metal (e.g., gold, platinum, palladium, chromium or titanium) or an electrically conductive metal oxide (e.g., tin oxide or indium oxide) or semiconductor. The insulating pattern 4 comprises a resist film, an insulating oxide (e.g., SiO or SiO₂ ) or a nitride (e.g., Si₃N₄ or BN). The insulated polymer film 5 is coated on the electrode substrate 10 by a proper method such as casting, spin coating or a doctor blade method. The insulated polymer film used in the present invention is selected from a polyvinyl chloride resin (i.e., polyvinyl chloride or a copolymer of vinyl chloride with other vinyl monomer), a polyvinylidene chloride resin (i.e., polyvinylidene chloride or a copolymer of vinylidene chloride with other vinyl monomer), a polyvinylidene fluoride resin (i.e., polyvinylidene fluoride or a copolymer of vinylidene fluoride with other vinyl monomer), a polystyrene resin (i.e., polystyrene or a copolymer of styrene with other vinyl monomer), an acrylic resin (i.e., polymethylacrylate or a copolymer of other acrylic monomer with other vinyl monomer), polyvinyl carbazole, a copolymer of vinyl carbazole with other vinyl monomer, a copolymer of ethylene with other vinyl monomer, polyvinyl acetate, a copolymer of vinyl acetate with other vinyl monomer, other polyvinyl alcohol, other polycarbonate, polyetherimide, other polyether sulfonate, other polyamide-imide, other nylon, other phenol resin, other polybutadiene rubber, ethyl cellulose, cellulose acetate, and cellulose nitrate. Additives such as a plasticizer, a heat stabilizer, a lubricant, an ultraviolet absorber, a defogging agent, a pigment, a dye, a surfactant, an electrically conductive filler and the like may be added to the polymer materials described above. A current flows between the electrically conductive layer 3 of the electrode substrate 10 and a counter electrode (not shown) located to oppose the electrode substrate 10 in an electrochemical polymerization solution to form an electrically conductive pattern made of an electrochemically polymerized aromatic polymer material on only the electrically conductive portion of the electrode. An aromatic compound subjected to electrochemical polymerization can be selected from the group consisting of pyrrole, 3-methylpyrrole, N-methylpyrrole, thiophene, furan, phenol, thiophenol, selenophene, tellurophene, biphenyl, azulene, p-terphenyl, o-terphenyl, p-quaterphenyl, 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-furyl-α-thienylselenide, 2-(2-pyrrolyl)selenophene, 2-(2-selenienyl)tellurophene, N-vinylcarbazole, N-ethynylcarbazole, methylazulene and pyrene. A compound such as an organic quaternary ammonium salt, protonic acid or an inorganic salt is used as an electrolyte in electrochemical polymerization. As a solvent for dissolving an aromatic compound to be electrochemically polymerized, an acetonitrile, benzonitrile, or propylene carbonate based solution is normally used and the solvent composition is adjusted in accordance with the type of insulated polymer film to be rendered electrically conductive. This selection must be made such that an aromatic compound and electrolytic anions are diffused in the film to progress polymerization without dissolving the insulated polymer film. The polymer film is peeled to obtain a polymer film having a desired electrically conductive pattern. When the conductive and insulating patterns are formed on the electrode in order to obtain the electrically conductive film in the manner as described above, an insulating polymer film portion which contacts the electrically conductive portion of the electrode is made conductive. Another insulating polymer film portion which contacts the insulating portion of the electrode is kept insulative. In this process, the entire film can be easily peeled from the electrode. Once the pattern is formed on the electrode surface, the electrode can be repeatedly used. In addition, when the electrode comprises a drum, the film with a conductive pattern can be continuously formed at low cost. In electrochemical polymerization of an aromatic compound on the electrode coated with an insulating film, both major surfaces or one major surface (the surface contacting the electrode surface) of the film can be made conductive in accordance with polymerization conditions. The present invention will be described in detail by way of examples. According to the present invention, the type of pattern, an insulating film material, a structure of the electrically conductive film can be modified to provide a virtually indefinite number of combinations. For example, as shown in Fig. 1C, the electrically conductive pattern is formed entirely from the upper surface to the lower surface of the film along the direction of thickness thereof. However, this conductive pattern can be formed from one surface of the film to a certain depth. Therefore, the present invention is not limited to the following examples. Example 1 A 1,000-A indium oxide film was sputtered on a glass substrate. A one-dimensional grating pattern was formed on the electrically conductive substrate having the indium oxide layer thereon in the following manner. A 2-µm photoresist AZ-1350J (Shipley Corp.) was spin coated on the indium oxide layer and was exposed with a photomask having a one-dimensional grating pattern with 0.1-mm wide stripes separated by 0.1-mm wide spaces. A 2,000-A SiO film was deposited to the exposed photoresist film and was lifted off in methyl ethyl ketone to prepare an SiO pattern as an insulating layer having a 0.1-mm width at 0.2-mm pitches on the indium oxide layer. Casting was performed using a solution of polyvinyl chloride (molecular weight: 700,000) in methyl ethyl ketone to obtain a 20-µm film on the substrate. The substrate with the film was dipped in an electrolytic solution obtained by dissolving 0.3 mol/ℓ of tetraethylammonium paratoluenesulfonate and 1 mol/ℓ of pyrrole in an acetonitrile-methyl ethyl ketone (1 : 1) solvent mixture. In this case, a titanium mesh plated with platinum was used as the counter electrode. Electrochemical polymerization of pyrrole was performed at a voltage of 3.0 V for 10 minutes, thereby precipitating black polypyrrole. The resultant film could be easily peeled from the electrode. An electrical conductivity of the film was measured to be as high as 4.5 S/cm along a direction parallel to the stripes of the electrode. However, a portion of the film had an insulating property of 10⁻¹³ S/cm or less in a direction perpendicular to the stripes. As a result, an electrically insulated film with high anisotropy was prepared. Example 2 After 100-A ° chromium and 700-A ° platinum were deposited on a glass substrate, respectively, a 500-A ° ITO (indium-tin oxide) was sputtered on the resultant structure to prepare an electrically conductive substrate. A 2-µm photoresist AZ-1350J (Shipley Corp.) was spin coated on the ITO layer and was exposed with a photomask having a two-dimensional grating pattern having 50-µm pitches. The exposed photoresist film was developed, and then a 2,000-A ° silicon oxide (SiO) film was deposited thereon. The lift-off was performed in the methyl ethyl ketone solution. A two-dimensional pattern of the SiO layer as the insulating layer was formed on the electrically conductive ITO layer. Conductive island regions at an interval of 50 µm were formed on the surface of the ITO layer. A 15-µm vinylidene chloride-vinyl chloride (75 : 25) copolymer film was coated by casting on the substrate. The substrate with the film was dipped in an acetonitrile-tetrohydrofuran (2 : 1) solution containing thiophene (1 mol/ℓ) and tetraethylammonium perchlorate (0.3 mol/ℓ). A titanium mesh electrode plated with platinum was also dipped in this solution to perform electrochemical polymerization of thiophene at a voltage of 4.0 V for 10 minutes. As a result, green polythiophene was precipitated, and its film was peeled from the electrode substrate. An electrical conductivity of a portion as the upper surface of the film was 10⁻¹² S/cm or less and regarded as an insulating property. An electrical conductivity of the film along the direction of thickness thereof was as high as 1.5 S/cm. As a result, a film having conductivity only along the direction of thickness was prepared. An electrode resistance is one of the polymerization parameters. When an electrode substrate having a low resistance is used, the two major surfaces of the film can be easily made conductive. However, when an electrode substrate having a high resistance is used, only one major surface described above can be easily made conductive. By utilizing this property, when an electrode substrate having a low-resistance portion and a high-resistance portion is used, a lower surface of the film which contacts the electrode surface is entirely made conductive. However, in the surface which contacts with the electrochemical polymerization solution, only the low-resistance portion is made conductive. Such an example will be described in Example 3. Example 3 After 100-A ° chromium and 1,000-A ° gold were deposited on a glass substrate, respectively, a 2,000-A ° ITO layer was deposited thereon. A 2-µm photoresist AZ-1350J was spin coated on the ITO layer and was exposed with a photomask to form a one-dimensional stripe pattern having stripes of 50 µm separated by spaces of 50 µm. The photoresist film was then developed, and the ITO layer was etched for 1,200 A ° in a parallel-plate type reactive ion etching apparatus using an etchant of CBrF₃ at a flow rate of 20 SCCM, a pressure of 20 mTorr and a power of 100 W. When the residual AZ photoresist film was removed by a plasma asher apparatus, an electrode substrate was prepared wherein ITO oxide layers having thickness of 800 A ° and 2,000 A ° ware alternately formed on the gold layer at intervals of 50 µm. A 20-µm polyvinyl chloride (molecular weight: 70,000) film was formed by casting on the resultant electrode substrate. Electrochemical polymerization of pyrrole was performed for the electrode with the film in the same manner as in Example 2. Polypyrrole was precipitated on the entire surface of the film. The polypyrrole film could be easily peeled from the electrode substrate. A surface of the film which contacted the electrode substrate had a high electrical conductivity of 12 S/cm in a direction parallel to the one-dimensional stripe pattern and a high electrical conductivity of 8.5 S/cm in a direction perpendicular thereto. However, a surface of the polypyrrole film which contacted the electrolytic solution had a high conductivity of 6.8 S/cm in a direction parallel to the stripes but had an insulation of 10⁻¹² S/cm or less in the direction perpendicular thereto. In this manner, when the electrically conductive patterns having different resistivities were formed on the electrode surfaces and the electrochemical polymerization conditions were properly selected, one surface was made entirely conductive, and the other surface had an anisotropic conductivity pattern. As described above, a polymer film is coated on an electrode with a desired electrically conductive pattern, and an aromatic compound is electrochemically polymerized to obtain a polymer film having the same pattern as the electrically conductive pattern of the electrode, thereby easily manufacturing a film having anisotropic conductivity or a special electrically conductive pattern. The resultant films can be used in a variety of applications for components much, as patterned electrically conductive layers of two-dimensional input devices, input terminals of display elements and output terminals of image sensors. Referring to Fig. 1, the electrically conductive pattern constituting the electrode substrate 10 is obtained such that the insulated pattern 4 is formed on the electrically conductive layer 3. However, as shown in Fig. 2, an electrically conductive pattern 2 may be directly formed on an insulating substrate 1. In addition, the electrode with the conductive pattern described above may comprise a drum-like structure for continuously forming a polymer film with a conductive pattern. A simplified electrode structure for forming a film with a conductive pattern will be described hereinafter. A material such as a semi-insulating semiconductor material is used wherein a high electrical resistance is given in a dark state without light exposure but the surface resistance is decreased, so that a portion subjected to light exposure can be made conductive. Therefore, the portion subjected to light exposure is limited to obtain a polymer film having a desired conductive pattern. The above technique is illustrated in Figs. 3A to 3C. Referring to Figs. 3A to 3C, an insulated polymer film 26 is coated on a major surface of a semi-insulating semiconductor substrate 25 serving as an electrode substrate. When the substrate 25 with the insulating polymer film 26 is irradiated with light using a pattern mask 27, a current required for electrochemical polymerization flows in only the exposed portion, thereby obtaining an electrically conductive area 28 (indicated by hatched lines) in the polymer film 26. Thereafter, the polymer film 26 is peeled from the electrode to prepare a polymer film with a conductive pattern shown in Fig. 3C. According to this method, the flat surface of the electrode can be used, and the patterning of electrode substrate is not necessary. In addition, the resultant film can be easily peeled from the electrode, because of no pattern on the electrode. The above embodiment will be described in detail by way of examples. However, the present invention is not limited to these examples. Example 4 When 1-µm amorphous silicon was deposited by CVD on a stainless steel plate, the amorphous silicon film had a resistivity of about 10⁸ Ωcm in a dark state. 1-µm polyvinyl chloride was spin coated on the amorphous silicon film. An insulating rubber resin was coated on a surface of the stainless steel plate which did not have the amorphous silicon film thereon. The resultant substrate was dipped together with a platinum counter electrode in an electrolytic solution obtained by dissolving 0.3 mol/ℓ of tetraethylammonium paratoluenesulfonate and 1 mol/ℓ of pyrrole in an acetonitrile-tetrahydrofuran (2 : 1) solvent mixture. A voltage of 1.2 V was applied between the film coated with the polyvinyl chloride film and the platinum counter electrode. An argon laser beam having a spot diameter of 50 µm irradiated the amorphous silicon substrate through the polyvinyl chloride for 50 stripes with a pitch of 200 µm at a scan speed of 1 m/min. As a result, a polypyrrole was formed in the irradiated area, and a polymer film having the polypyrrole or conductive pattern was obtained. The resultant film was peeled from the amorphous silicon substrate. An electrical conductivity of the film was measured by-a 4-terminal method in a direction parallel to the polypyrrole stripes to obtain a high conductivity of 10 S/cm. However, when an electrical conductivity of the film was measured in a direction perpendicular to the polypyrrole stripes, an insulating property was given as 10⁻⁸ S/cm or more. Example 5 An amorphous silicon film was deposited on a stainless steel plate, polyvinyl chloride was coated on the amorphous silicon film with a thickness of about 1 µm, and an insulating rubber resin was coated on a surface of the stainless steel plate which did not have the amorphous silicon film thereon, thereby obtaining a substrate in the same manner as in Example 4. A photomask having a stripe pattern with a 50-µm width and a 200-µm pitch was brought into contact with the polyvinyl chloride coated on the substrate. The substrate with the photomask was dipped together with a platinum counter electrode in an electrolytic solution obtained by dissolving 0.3 mol/ℓ of tetraethylammonium paratoluenesulfonate and 1 mol/ℓ of pyrrole in an acetonitrile-tetrahydrofuran (2 : 1) solvent mixture. A voltage of 1.6 V was applied between the film coated with the polyvinyl chloride film and the platinum counter electrode. Light from a high-voltage mercury lamp irradiated the polyvinyl chloride film for 100 seconds to grow a polypyrrole pattern in the polyvinyl chloride film, thereby preparing a polymer film with a conductive pattern. The resultant film was peeled from the amorphous silicon substrate. An electrical conductivity of the film was measured to be as high as 20 S/cm by a 4-terminal method in a direction parallel to the polypyrrole stripes. However, when an electrical conductivity of the film was measured in a direction perpendicular to the polypyrrole stripes, an insulating property was given as 10⁻⁸ S/cm or more. According to the present invention as described above, a polymer film was coated on a substrate whose electrical resistance is decreased upon light exposure, and light irradiates the film in a desired pattern. The exposed portion is used as an electrode, and electrochemical polymerization is performed, thereby easily preparing a film having anisotropic conductivity or a special conductive circuit pattern. The film with the conductive pattern described above comprises a hybrid structure of an insulating polymer and an electrically conductive polymer, so that the electrical conductivity is degraded as compared with the electrochemical polymer. When an electrically conductive pattern becomes narrow, its electrical resistance is increased. In this sense, a range of applications of the film is often limited. In order to solve this problem, an electrically conductive portion is obtained by laminating an electrically conductive layer made of an electrochemically polymerized aromatic compound and a layer obtained by mixing an electrochemically polymerized aromatic compound in an insulating polymer film. Figs. 6A to 6F are sectional views for explaining the steps in manufacturing a polymer film having an electrically conductive pattern. As shove in Fig. 6A, an electrode substrate 14 is dipped together with a counter electrode in an electrochemical polymerization solution of an aromatic compound. A DC voltage is applied between the electrode substrate 14 and the counter electrode. An electrochemical polymer layer 11 of an aromatic compound is formed in correspondence with the conductive electrode pattern (Fig. 6B). The electrode substrate 14 shown in Fig. 6A is constituted by the insulating substrate of Fig. 1A, the electrically conductive layer formed thereon and the insulating pattern formed on the electrically conductive layer. Alternatively, as shown in Fig. 2, the electrode substrate may be constituted by the electrically conductive layer directly formed on the insulating substrate. Subsequently, an insulating polymer film 13 is formed on the electrode substrate (Fig. 6C). The electrode substrate with the film is dipped in an electrochemical polymerization solution again to perform electrochemical polymerization of an aromatic compound. An electrochemical polymer is grown from an insulating polymer film portion contacting the single electrochemical polymer layer formed in the electrically conductive pattern of the electrode substrate and is formed in the insulating polymer film, thereby obtaining an electrically conductive polymer layer 12 (Fig. 6D). In this case, when electrochemical polymerization is stopped at its early stage, a film with an electrically conductive pattern is formed on only one major surface, as shown in Fig. 5. However, when electrochemical polymerization is sufficiently performed, a film with electrically conductive patterns on both the major surfaces of Fig. 4 is obtained. The resultant film is peeled from the electrode substrate (Fig. 6E). The laminated conductive patterns have good adhesion strength, so that a single electrochemical polymer layer will not be removed from the insulating polymer film due to the following reason. After the insulating polymer film is adhered to the electrochemical polymer layer, electrochemical polymerization is started from the single electrochemical polymer layer, and the electrochemical polymers are bonded to each other. Figs. 4 and 5 show a polymer film structure having an electrically conductive pattern of the present invention. An electrically conductive pattern comprises a laminate of a single electrochemical polymer layer 11 of an aromatic compound and an electrically conductive polymer layer 12 obtained by combining the insulating polymer film material and the electrochemical polymer, and the electrically conductive pattern is formed in the insulating polymer film 13. The single electrochemical polymer layer 11 decreases a surface resistance of the electrically conductive pattern, and the polymer layer 12 increases adhesion strength between the single electrochemical polymer layer and the insulating polymer film and increases the thickness of the electrically conductive pattern. In addition, the insulating polymer film holds the electrically conductive pattern and increases the mechanical strength of the film. The polymer layer 12 comprises a layer which is entirely conductive as shown in Fig. 4 or a layer whose one surface is made conductive as shown in Fig. 5. Either type of polymer layer 12 can be used for a desired application. Other examples of the present invention will be described hereinafter. Example 6 A chromium layer of 15 nm was deposited on a glass substrate having an ITO layer and a surface resistance of 10 Ω to prepare an electrode substrate. A 3.5-µm SiO₂ film was sputtered on the substrate. A 2-µm photoresist AZ-1350 (Shipley Corp.) was spin coated on the SiO₂ film. By using a photomask having a one-dimensional stripe pattern with a stripe width of 10 µm and a space of 40 µm between the stripes, the photoresist layer was exposed and developed to obtain a photoresist pattern. The SiO, film was etching by plasma etching using CF₄ gas as an etchant and the photoresist pattern as a mask. The photoresist pattern was then removed to form SiO₂ stripes on the chromium-ITO surface. The SiO₂ stripes had a width of 10 µm and formed at a rate of 50 stripes per millimeter. A solution of pyrrole (1 mol/ℓ) and tetraethylammonium paratoluenesulfonate (0.3 mol/ℓ) in acetonitrile-nitrobenzene (4 : 1) was prepared as an electrochemical polymerization solution. The resultant electrode substrate as an anode and a platinum-plated titanium mesh electrode as a cathode were dipped in the above solution. A DC voltage of 2 V was applied between the cathode and the anode while a charge density was kept at 0.6 coulomb/cm², thereby performing electrochemical polymerization of pyrrole and hence obtaining polypyrrole having a thickness of 2 µm and not covered with SiO₂ . A methyl ethyl ketone solution of polyvinyl chloride (molecular weight: 70,000) was casted on the polypyrrole film having a thickness of 2 µm, thereby forming a polyvinyl chloride film having a thickness of 20 µm. The electrode substrate with the film was dipped together with a platinum-plated titanium mesh electrode in the electrolytic solution of pyrrole. A DC voltage of 1.5 V was then applied between the electrode substrate and the mesh electrode while a charge density of 0.15 coulomb/cm² was kept to perform pyrrole polymerization. The film after polymerization was washed with ethanol and dried. The dried film was peeled from the electrode substrate. The polypyrrole film which was first obtained was not left on the electrode substrate. The polyvinyl chloride film was strongly adhered with the patterned polypyrrole film. Upon peeling of the film, surface resistances of a surface (to be referred to as an electrode contact surface) of the film which contacted the electrode along the direction parallel to the stripes and perpendicular thereto were measured by a 4-terminal method. The surface resistances of the film along the parallel and vertical directions were 15 Ω and 20 MΩ or more, respectively. As a comparative example, a polyvinyl chloride film having a thickness of 20 µm was directly formed on the electrode substrate used in the above embodiment. Electrochemical polymerization of pyrrole was performed on the electrode with the film at a voltage of 1.5 V and a charge density of 0.15 coulomb/cm². The surface resistances of the film along directions parallel to and perpendicular to the stripes were 3.5 kΩ and 20 MΩ, respectively. In the manner as described above, after the patterned polypyrrole film was formed on the substrate, a polymer film with a conductive pattern was formed on the polypyrrole film to decrease the surface resistance to be about 1/100. Example 7 A platinum film having a thickness of 20 nm was deposited on a glass substrate having a surface resistance of 10 Ω and an ITO layer. A 3-µm photoresist AZ-1350J (Shipley Corp.) was spin coated on the platinum film. The photoresist film was exposed by using a photomask having a one-dimensional pattern having a stripe width of 40 µm and a space of 10 µm between the adjacent stripes and was developed to obtain a photoresist pattern. A 2-µm SiO film was deposited to cover the entire surface of the substrate and was lifted off in methyl ethyl ketone, thereby obtaining a 50-stripes/mm SiO pattern having a stripe width of 10 µm. An acetonitrile solution of thiophene (0.8 mol/ℓ) and tetraethylammonium perchlorate (0.2 mol/ℓ) was prepared as an electrochemical polymerization solution. The electrode substrate as an anode and a platinum-plated titanium mesh electrode as a cathode were dipped in the above solution. A DC voltage of 5 V was applied between the anode and the cathode while a charge density of 0.7 coulomb/cm² was kept to electrochemically polymerize thiophene, thereby forming a 1.8-µm polythiophene film on the platinum/ITO pattern. A cyclohexanone solution of polyvinylidene chloride was casted on the substrate to form a 30-µm polyvinylidene chloride film. The resultant electrode substrate with the film was dipped together with a platinum-plating titanium mesh electrode in the electrolytic solution of thiophene. A DC voltage of 3 V was applied between the electrode substrate and the mesh electrode while a charge density of 0.2 coulomb/cm² was kept to perform polymerization of thiophene. After polymerization, the film was washed with ethanol and dried. The dried film was peeled from the electrode substrate. The polythiophene film first formed was not left between the patterns on the electrode substrate. The polyvinylidene chloride film was strongly adhered with the polythiophene film. The peeled film was subjected to surface resistance measurement by a 4-terminal method. Surface resistances of the film along directions parallel and perpendicular to the stripes and the vertical direction were 130 Ω and 20 MΩ or more, respectively. As a comparative example, a polyvinylidene chloride film having a thickness of 30 µm was formed directly on the same electrode substrate as this Example. On the electrode with the film, thiophene was electrochemically polymerized at a voltage of 3 V and a charge density of 0.2 coulomb/cm². The surface resistances of the resultant film along directions parallel and perpendicular to the stripes were measured to be 6.5 kΩ and 20 MΩ or more, respectively. In this manner, after the patterned polythiophene film was formed, the polymer film with a conductive pattern was formed thereon to decrease the surface resistance of the patterned electrically conductive film to about 1/10. Example 8 An acetonitrile-nitrobenzene (4 : 1) solution of pyrrole (1 mol/ℓ) and tetraethylammonium tetrafluoroborate (0.3 mol/ℓ) was prepared as an electrochemical polymerization solution. An electrode substrate as an anode and a platinum-plated titanium mesh electrode as a cathode in the same manner as in Example 1 were dipped in the above solution A DC voltage of 2 V was applied between the anode and the cathode while a charge density of 0.6 coulomb/cm³ was kept to electrochemically polymerize pyrrole, thereby forming a 2-µm polypyrrole layer on the conductive portion on the electrode substrate. A tetrahydrofuran solution of polystyrene (molecular weight: 800,000) was casted on the surface of the substrate to obtain a polystyrene film having a thickness of 4.5 µm. The resultant substrate with the film was dipped together with a platinum-plated titanium mesh electrode in an electrolytic solution of pyrrole. A DC voltage of 1.5 V was applied between the electrode substrate and the titanium mesh electrode while a charge density of 0.3 coulomb/cm² was kept to electrochemically polymerize pyrrole. After polymerization, the film was washed with ethanol and dried. The dried film was peeled from the electrode. The polypyrrole film first formed on the electrode was not left between the patterns on the electrode substrate. The polystyrene film was strongly adhered with the patterned polypyrrole film. After peeling of the film, the surface resistances of the electrode contact surface of the film along directions parallel and perpendicular to the pattern were measured by the 4-terminal method to be 10 Ω and 20 MΩ, respectively. As a comparative example, a polystyrene film having a thickness of 15 µm was formed directly on the same electrode substrate as in this Example. Pyrrole was electrochemically polymerized on the electrode substrate with the film at a voltage of 1.5 V and a charge density of 0.3 coulomb/cm² to form a polymer film with a conductive pattern. The surface resistances of the electrode contact surface of the film along directions parallel and perpendicular to the pattern were measured to be 280 Ω and 20 MΩ or more, respectively. As described above, after the patterned polypyrrole film was formed, the polymer film with a conductive pattern was formed thereon, thereby-decreasing the surface resistance of the patterned electrically conductive film to about 1/10. Example 9 A gold film having a thickness of 15 nm was deposited on a glass substrate having a surface resistance of 10 Ω and an ITO layer to prepare an electrode substrate. An SiO₂ film was sputtered on the electrode substrate to a thickness of 5 µm. A 3-µm photoresist AZ-1350J (Shipley Corp.) was spin coated on the SiO₂ film. The photoresist film was exposed with a photomask having a circular pattern with a diameter of 50 µm at lateral and vertical intervals of 200 µm and was developed to obtain a photoresist pattern. The SiO₂ film was plasma etched by using the photoresist pattern as a mask and CF₄ gas as an etchant. After the photoresist pattern was removed, an SiO₂ layer having apertures each having the diameter of 50 µm was formed on the surface of the gold-ITO surface. An acetonitrile-ethanol (4 : 1) solution of pyrrole (1 mol/ℓ) and tetraethylammonium paratoluenesulfonate (0.3 mol/ℓ) was prepared as an electrochemical polymerization solution. The electrode substrate as an anode and a platinum-plated titanium mesh electrode as a cathode were dipped in the solution. A DC voltage of 5 V was applied between the anode and the cathode while a charge density of 3 coulomb/cm² was kept to electrochemically polymerize pyrrole, thereby forming a 9-µm polypyrrole film on the electrode substrate. A dimethylformamide solution of polyvinylidene fluoride (molecular weight: 120,000) was casted on the electrode substrate to form a polyvinylidene fluoride film having a thickness of 12 µm. The substrate with the film was dipped together with a platinum-plated titanium mesh electrode in the electrolytic solution of pyrrole. A DC voltage of 3 V was applied between the electrode substrate and the mesh electrode while a charge density of 0.8 coulomb/cm² was kept to electrochemically polymerize pyrrole. After polymerization, the film was washed with ethanol and dried. The dried film was peeled from the electrode. In this case, the polypyrrole film first formed in a circular shape on the electrode was not left on the electrode. The polyvinylidene fluoride film was strongly adhered to the polypyrrole film. After peeling of the film, resistances of the surfaces of the film which contacted the electrode and the solution and the resistance of the film along a direction of thickness of the film were measured by the 4-terminal method. The surface resistances were 20 MΩ or more, and the resistance along the thickness direction were 25 Ω , respectively. The film having conductivity only along the thickness direction was prepared. As a comparative example, a polyvinylidene fluoride film having a thickness of 12 µm was directly formed on the same electrode substrate as in this Example. Pyrrole was electrochemically polymerized on the electrode substrate with the film at a voltage of 5 V and a charge density of 4 coulomb/cm² to prepare a polymer film with a conductive pattern. The surface resistances of the film which contacted the electrode and the solution and the resistance along the direction of thickness of the film were measured by the 4-terminal method. The surface resistances of the two surfaces were 20 MΩ or more, and the resistance along the thickness of the film were 55 Ω. In this manner, the resultant film had conductivity only along the thickness direction. As is apparent from the above description, after the circular polypyrrole pattern was formed, the polymer film with a conductive pattern was formed thereon. The resistance along the thickness direction can be decreased to about 1/10, thereby obtaining the film having conductivity only along the thickness direction. According to the above embodiment, an electrochemical polymer layer of an aromatic compound was formed on the electrode having a predetermined electrically conductive pattern, and then an insulating polymer film was formed thereon to electrochemically polymerize the aromatic compound, thereby forming the insulating polymer film-electrochemically polymer layer. As a result, a polymer film having a low electrical resistance was prepared. Figs. 7A to 7D show still another embodiment of the present invention. Referring to Figs. 7A to 7D, reference numeral 30 denotes an insulating substrate; 31, an electrically conductive layer for constituting an electrode; 32, an insulating pattern; 33, an insulating polymer film; and 34, a conductive polymer film. Fig. 8 shows an electrode pattern having regular linear conductive portions. Referring to Fig. 7A, the insulating pattern 32 is formed on the surface of the low-resistance electrode 31 formed on the insulating substrate 30 to leave linear gaps. The polymer film 33 is formed on the surface of the resultant structure, as shown in Fig. 7B. When the aromatic compound is electrochemically polymerized on the electrode substrate described above, an electrical current is concentrated in the gaps to progress electrochemical polymerization. As shown in Fig. 7C, the conductor paths reaching the film surface are formed. At the same time, electrochemical polymerization is slightly progressed in the lateral direction. Electrochemical polymerization is stopped after a proper period of time, and the polymer film 34 is removed from the electrode substrate, as shown in Fig. 7D. Although the portions near the gaps are made highly conductive, the intermediate portions are kept at low conductivity but have a high light transmittance. In other words, light transmissivity can be guaranteed in the film as a whole. In particular, when an antistatic transparent film is manufactured by using the above film, an internal object can be visually observed. The transmittance can be controlled by controlling the width of the gaps and their pitches, in addition to controlling the electrochemical polymerization conditions. The pitch must be optimized in consideration of a thickness of a film to be made conductive. In order to obtain uniform electrical conductivity and uniform transmittance along a film surface, the gaps must be uniformly and regularly formed. For this purpose, a hexagonal or honneycomb structure (Fig. 8) or an octagonal structure is preferred. When the current is to be concentrated, the gap width is less than 10 µm and more preferably 5 µm or less. The pitch between the gaps preferably corresponds to the thickness of the polymer film to be made conductive. Unless the pitch is at least 20 µm or more, a sufficiently high transmittance cannot often be obtained. In order to form a linear conductive pattern, a photomask having the identical pattern as described above must be used. The pattern is transferred to the resist film to pattern the insulating film in accordance with a lift-off or etching technique. In order to obtain a gap having a width of 2.0 µm or less, electron beam exposure or X-ray lithography must be used. Examples associated with the embodiment described with reference to Figs. 7 and 8 will be described hereinafter. Example 10 A NESA glass substrate having a surface resistance of 10 Ω/cm² was used as an electrode substrate. A 1.2-µm photoresist AZ-1350J (Shipley Corp.) was spin coated on the NESA glass substrate. The pattern having a stripe width of 2 µm and an interval of 18 µm, as shown in Fig. 8, was transferred to the photoresist film by using a photomask. The photoresist film was developed to obtain a photoresist pattern. A 0.25-µm SiO film was thermally deposited on the entire surface of the substrate. The SiO film was lifted off in an acetone solution to obtain the SiO islands forming a gap of about 2 µm. An N,N-dimethylformamide solution of polyvinylidene fluoride was casted on the resultant structure to form a polyvinylidene fluoride film having a thickness of 20 µm. An acetonitrile-ethyl alcohol (2 : 1) solution of pyrrole (1.2 mols/ℓ) and tetraethylammonium tetrafluoroborate (0.3 mol/ℓ) was prepared as an electrochemical polymerization solution. The electrode substrate with the film was dipped together with a platinum-plated mesh counter electrode in the above solution. A voltage of 3 V was applied between the electrode substrate and the counter electrode for 2 minutes to electrochemically polymerize pyrrole. After electrochemical polymerization, the film could be easily peeled from the electrode. A resistance of the film and its transmittance at a wavelength of 600 nm were measured. The results are summarized in Table 1. *1 The upper surface is defined as a surface of the film which contacts the electrode and the lower surface is defined as a surface which is opposite to the upper surface, and a square indicates 1 cm². As is apparent from Table 1, an electrically conductive film had a low surface resistance and a high transmittance. This film also had conductivity along the direction of thickness thereof. Example 11 The same electrode as in Example 10 was used in Example 11. A solution of polyvinyl chloride in a tetrahydrofuran-methyl ethyl ketone solvent mixture was casted to form a film having a thickness of 35 µm. The resultant substrate with the film was dipped together with a platinum-plated mesh counter electrode in an acetonitrile-nitrobenzene (1 : 1) solution of thiophene (1 mol/ℓ) and tetraethylammonium perchlorate (0.3 mol/ℓ). A DC voltage of 5.0 V was applied between the electrode substrate and the counter electrode for 2 minutes to electrochemically polymerize thiophene. The resultant film was easily peeled from the substrate. An electrical conductivity of the film and its transmittance at a wavelength of 600 nm were measured. The results are summarized in Table 2: As is apparent from Table 2, even if a film thickness was increased to 35 µm, the film had conductivity along the direction of thickness thereof as well as along the film surfaces. In addition, this film had a high transmittance. According to the examples described above, a polymer film is formed on the electrode having a regular linear conductive portion, and the aromatic compound is electrochemically polymerized, so that the conductive electrochemical polymer is immediately grown from the polymer film portion which contacts the linear conductive portion, thereby making the entire film conductive. The film portion contacting the linear portion is rendered highly conductive, but the film has a high transmittance when the electrochemical polymerization conditions are optimally set. The electrically conductive film having a high transmittance can be used as an antistatic preventing wrapping film, an input/output device transparent conductive film, or the like. In the above embodiments, a single polymer film is used as the insulating polymer film. However, the insulating polymer film may comprise a multilayer film having at least two polymer films. In this case, adhesion and conductivity are further improved. A material to be removed from the polymer coated on the electrode substrate may be contained in the polymer. Before and/or during reaction of the electrochemical polymerization, this material may be removed to easily diffuse the electrolyte or aromatic compound. In this case, when the material is removed, microvoids are formed in the polymer film. For this reason, the electrolyte and aromatic compound can be easily diffused in the film, thereby increasing polymerization speed and providing a patterned electrically conductive polymer film. When a porous polymer film is used, the resultant patterned electrically conductive polymer film has a uniform thickness. When an electrochemical polymer of an aromatic compound is mixed in a surface layer of the polymer film, electrochemical polymerization can be performed using the obtained sheet. More particularly, electrodes shown in Fig. 1A or 2 may be brought into tight contact with two surfaces of the polymer film, and a voltage is applied therebetween to perform electrochemical polymerization of the aromatic compound. In this manner, the film has a high conductivity on the surface thereof.

Claims: A polymer film containing a conductive pattern characterized in that it comprises a film of an insulating polymer (5) which includes pattern areas (6) defined by the presence of an electrically conductive polymer of an aromatic compound, rendered electrically conductive by in situ polymerization, and non-pattern areas defined by the absence of the said conductive polymer, the conductive pattern (6) having an internal portion extending into the thickness of the film from at least one major surface of said film (5). A film as claimed in Claim 1, characterized in that said insulated polymer film (5) is a polyvinyl chloride resin, polyvinylidene chloride resin, polyvinylidene fluoride resin, polystrene resin, acrylic resin, polycarbazole, a polymer of vinyl carbazole with another vinyl monomer, a copolymer of ethylene with another vinyl monomer, polyvinyl acetate, copolymer of vinyl acetate with another vinyl monomer, polyvinyl alcohol, polycarbonate, polyetherimide, polyethersulfonate, polyamide-imide, nylon, phenol resin, polybutadiene rubber, ethyl cellulose, cellulose acetate, or cellulose nitrate. A film as claimed in Claim 2, characterized in that said polymer film contains an additive selected from a plasticizer, heat stabilizer, lubricant, ultra-violet absorber, defogger, pigment, dye, surfactant, and an electrically conductive filler. A film as claimed in any one of the preceding Claims, characterized in that said insulated polymer film is a multilayer film comprising at least two laminated polymer films. A film as claimed in any one of the preceding Claims characterized in that another electrically conductive layer of an electrochemical polymer of an aromatic compound is formed on said electrically conductive pattern on said surface of said insulating polymer film. A film as claimed in any one of the preceding Claims characterized in that said electrically conductive pattern comprises a regular linear pattern. A film as claimed in any one of the preceding Claims, characterized in that said aromatic compound is pyrrole, 3-methylpyrrole, N-methylpyrrole, thiophene, furan, phenol, thiophenol, selenophene, tellurophene, biphenyl, azulene, p-terphenyl, o-terphenyl, p-quaterphenyl, 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 -furyl-α -thienylselenide, 2-(2-pyrrolyl)-selenophene, 2-(2-selenienyl) tellurophene, N-vinyl-carbozole, N-ethynylcarbazole, methylazulene or pyrene. A method of manufacturing an insulating polymer film which has an electrically conductive pattern therein characterized by the steps of:- i) establishing the polymer film (5) on a major surface of an electrode (3,4;1,2) having an electrically conductive portion and an insulating portion; ii) causing an electrolyte solution and an aromatic compound to diffuse within the polymer film through to the said major surface; iii) electrochemically polymerizing the aromatic compound pattern-wise at the major surface to form the said electrically conductive pattern (6) in the polymer film (5) at a portion which contacts said electrically conductive portion of the electrode (3,4;1,2); iv) continuing the electrochemical polymerization step to cause the interface between the conductive pattern (6) and the insulating polymer material to advance through the thickness of the polymer film (5), away from the said major surface. A method according to Claim 8, characterized in that the major surface of said electrode exhibits an electrically conductive pattern (2). A method according to Claim 8 or 9, characterized in that said insulating polymer film is a material according to Claim 2. A method according to Claim 10, characterized in that said polymer film contains an additive according to Claim 3. A method according to any one of Claims 8 to 11, characterized in that said insulating polymer film is a multilayer film comprising at least two laminated polymer films. A method according to any one of Claims 8 to 12, characterized in that an electrolyte selected from an organic quaternary ammonium salt, a protonic acid and an inorganic salt, is employed during electrochemical polymerization. A method according to Claim 13, characterized in that a solvent for dissolving the aromatic compound to be electrochemically polymerized with said electrolyte, is selected from acetonitrile, benzonitrile and propylene carbonate electrolytes, to be compatible with said insulating polymer film to be made conductive. A method according to any one of Claims 8 to 14, characterized in that said electrode comprises a substrate (1), an electrically conductive layer (3) formed thereon, and an insulating pattern (4) formed on the conductive layer to create with the conductive layer the said major surface of the electrode. A method according any one of Claims 8 to 15, characterized in that said electrode includes a layer (25) whose electrical resistance varies with intensity of light radiation incident thereupon, said layer being exposed pattern-wise to light to produce electrochemical polymerization in accordance with a pattern to be formed in said polymer film.

Inventors: HIKITA, MAKOTO, NIWA, OSAMU, SUGITA, AKIO, TAMAMURA, TOSHIAKI
Applicants: NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Application year: 1985
Main classification: H05K3
IPC codes: H05K3