1. Field of the Invention
This invention relates to a method for producing a soluble conductive polymer which is soluble in a solvent.
A solution comprising this soluble conductive polymer as the main component can be used for forming a conductor by a simple method such as a spray coating method, a dip coating method, a roll coating method, a gravure coating method, a reverse roll coating method, an air-knife coating method, a curtain coating method or the like on various substrates. The above solution can also be used in admixture with a suitable binder polymer for increasing the adhesiveness of a conductive film and the strength of a coating film.
As the substrate to be coated, there are mentioned various plastics, for example, polyester resins such as polyethylene terephthalate (PET), polyethylene-naphthalate (PEN) and the like, polyethylene, polypropylene, polyvinyl chloride, nylon, polystyrene, polycarbonate, epoxy resins, fluoroplastics, polysulfone, polyimide, silicone resins, polyurethane, phenol resins, and the like; molded articles and films of these plastics such as synthetic papers and the like; paper; iron; aluminum; copper; zinc; nickel; stainless steel; and the like. The coating step may be conducted in the course of the production of these substrates, for example, before or during a monoaxial stretching step, a biaxial stretching step, a molding step, an embossing step or the like, or can be applied to a substrate which has been subjected to these treatment.
Moreover, a composition comprising the above soluble conductive polymer as the main component can be applied to various antistatic agents, condensers, batteries, EMI shields, chemical sensors, display devices, nonlinear molding materials, anticorrosive agents, adhesives, fibers, antistatic coating compositions, electro-coating compositions, plating primer, electrostatic coating primer, electric prevention for corrosion, enhancement of the storing capacity of battery and the like. In addition, the above polymer is excellent in applicability to various antistatic uses because it has no moisture-dependency of conductivity, has a high transparency and can be subjected to stretching, molding, embossing and the like.
The application of the soluble conductive polymer to antistatic uses includes packaging materials, magnetic cards, magnetic tapes, magnetic discs, photographic films, printing substrates, heat seal tapes and films, IC trays, IC carrier tapes, cover tapes and the like.
2. Description of the Related Art
Doped polyaniline has been well known as a soluble conductive polymer; however, it is insoluble in almost all general solvents except some nonprotonic polar solvents and hence has a difficulty in molding.
Moreover, though a process for producing a polyaniline by electrolytic oxidation polymerization [JP-A-60-235,831 and J. Polymer Sci. Polymer Chem. Ed., 26, 1531 (1988)] can form a film of polyaniline on an electrode, but has such a problem that its isolation operation becomes complicated and its mass production is difficult.
Proposals have recently been made for an alkali-soluble sulfonated polyaniline which develops conductivity without adding a doping agent and its synthesis method and for a carboxylated polyaniline and its synthesis method.
As a method for the synthesis of a sulfonated polyaniline, there are known, for example, a method for the synthesis of a sulfonated polyaniline by electrochemically polymerizing aniline and m-aminobenzenesulfonic acid (Journal of The Chemical Society of Japan, 1985, 1124 and JA-A-2-166,165), a method for the synthesis of a sulfonated polyaniline by electrochemically polymerizing an o-, m- or p-aminobenzenesulfonic acid alone [Lecture Preprint II in the 64th Autumn Annual Convention of The Chemical Society of Japan, 706 (1992)], a method for the synthesis of a sulfonated polyaniline by chemically polymerizing aniline and an o- or m-aminobenzenesulfonic acid (JP-A-1-301,714), a method for the chemical oxidation polymerization of an aminobenzenesulfonic acid compound or monomers comprising an aminobenzenesulfonic acid compound and an aniline compound (JP-A-6-56,987), a method for the sulfonation with conc. sulfuric acid of an emeraldine type polymer (polyaniline) obtained by chemical or electrochemical polymerization (JP-A-58-210,902), a method for the sulfonation with sulfuric anhydride/triethyl phosphate complex (JP-A-61-197,633), a method for the sulfonation with fuming sulfuric acid [J. Am. Chem. Soc., (1991) 113, 2665-2671, J. Am. Chem. Soc., (1990) 112, 2800 and WO91-06887], a method for the synthesis of a sulfonated polyaniline of the N-substitution type by chemically polymerizing diphenylamine-4-sulfonic acid (sodium salt) [Polymer, (1993) 34, 158-162] and the like.
In J. Am. Chem. Soc., (1991) 113, 2665-2671, it is reported that the chemical and electrochemical polymerization of o- or m-aminobenzenesulfonic acid was tried but was not successful.
Furthermore, JP-A-6-56,987 states that when an aminobenzenesulfonic acid compound is or an aminobenzenesulfonic acid compound and an aniline compound are subjected to chemical oxidative polymerization in all of the acidic, neutral and alkaline solutions, a soluble conductive polymer which is soluble in water is obtained, and shows polymerization examples in sulfuric acid-acidic solution. However, in said publication, there is no statement of the molecular weight and other physical properties of the polymer, and hence, it is not clear what physical properties the polymer has. According to the present inventors' duplication, no polymer having a sufficiently large molecular weight for forming a film was able to be obtained. Moreover, when the present inventors have tried polymerization in an aqueous solution containing a protonic acid using sodium peroxodisulfate as an oxidizing agent, a polymer soluble in water was obtained but the molecular weight of the polymer was low and no practicably usable polymer for forming a film was able to be obtained.
Furthermore, the present inventors have duplicated the method for chemically polymerizing aniline and m-aminobenzenesulfonic acid with ammonium peroxodisulfate stated in JP-A-1-301,714 and the method for chemically polymerizing aniline and m-aminobenzenesulfonic acid with potassium permanganate stated in JP-A-6-56,987, to find that the sulfonic acid group has been introduced only in a proportion of about one sulfonic acid group per 5 aromatic rings in the polymer, and the polymer exhibited high conductivity but was completely insoluble in neutral or acidic water and substantially insoluble in an alkaline aqueous solution such as ammonia water. Moreover, when the sulfonation has been effected according to the method of JP-A-61-197,633, the solubility of the polyaniline in the sulfonation solvent has not been sufficient and the sulfonation reaction has proceeded in the dispersion state of the polymer, so that the sulfonic acid group has been introduced only in a proportion of about 1 group per 5 aromatic rings as described on page 7 of the same publication. The thus obtained sulfonated polyaniline in which the proportion of the sulfonic acid group introduced is small has such a problem that the conductivity and solubility are not sufficient.
In addition, J. Am. Chem. Soc., 113, 2665-2671 (1991) and J. Am. Chem. Soc., 112, 2800 (1990) state that when polyaniline is sulfonated with fuming sulfuric acid, the sulfonic acid group is introduced in a proportion of about one sulfonic acid group per two aromatic rings. However, when the polyaniline has been tried to be sufficiently sulfonated according to the above-mentioned method, a large excess of fuming sulfuric acid has become necessary because the solubility of the polyaniline in fuming sulfuric acid has not been sufficient. Moreover, there is also such a problem that when the polyaniline is added to fuming sulfuric acid, the polymer is easy to solidify. In addition, there is such a problem that the polymer synthesized by the above-mentioned method and its sulfonated product are dissolved in an aqueous solution containing a base such as ammonia, an alkylamine or the like but not dissolved in water alone.
Also, Polymer, 34, 158-162 (1993) describes that when diphenylamine-4-sulfonic acid (sodium salt) is polymerized, an N-position-substituted type sulfonated polyaniline in which the benzenesulfonic acid group has been introduced in a proportion of one group per aniline skeleton is obtained, and this is dissolved in water alone, but ultracentrifugal operation is required for the isolation of the polymer. According to the present inventors' duplication, the yield of the polymer taken out of the polymerization solvent has been low because of the high solubility of the polymer in the solvent, and when no high speed centrifugal operation has been effected, it has been impossible to isolate the polymer. Furthermore, since the polymer is of an N-position-substituted type, it has been lower in conductivity than the polymer synthesized by the method of J. Am. Chem. Soc., 113, 2665-2671 (1991).
As a method for the synthesis of a carboxylated polyaniline, JP-A-4-268,331 proposes, for example, a production method in which 2- or 3-carboxyl group-substituted aniline or its salt is subjected to oxidative polymerization and then treated with a basic material to obtain a product in which the carboxyl group is in the form of a salt; however, the amount of the oxidizing agent used is required to be at least 2 equivalents per equivalent of the starting material and the electrical conductivity is low. From this fact, it is considered that the reactivity of monomer be low and a low molecular weight polymer have been produced.
JP-A-5-226,238 proposes a synthesis method in which methyl anthranilate (methyl ester of anthranilic acid) is polymerized in the presence of ammonium peroxodisulfate in an aqueous acidic medium and thereafter the methyl ester is saponified with alcoholic potassium hydroxide. However, since the reaction is effected two steps, the operation is very much complicated.
Further, the present inventors have tried to polymerize 2-carboxyl group-substituted aniline in an aqueous solution containing a protonic acid using ammonium peroxodisulfate as an oxidizing agent, but have not been able to obtain any product. They have also tried to polymerize aniline and a 2-carboxyl group-substituted aniline in an aqueous solution containing a protonic acid using ammonium peroxodisulfate as an oxidizing agent. However, a copolymer has been obtained, but the solubility and conductive thereof have been low. From this fact, it is considered that the copolymerization ratio of 2-carboxyl group-substituted aniline be low in the copolymer obtained.
When the moldability including film-formability by coating and the like are taken into consideration, particularly in order to make the polymer coatable on both hydrophilic and hydrophobic substrates, it is desired that the polymer is soluble in both water and organic solvent. However, the sulfonation product of polyaniline is soluble in alkaline aqueous solutions but insoluble in neutral to acidic aqueous solutions, and it cannot be said that the solubility in an organic solvent is sufficient.
As a method for solving these various problems, the present inventors have considered that in order to allow a polymer to exhibit conductivity without adding a doping agent and allow its solubility to be enhanced, it is necessary to introduce more acidic groups such as sulfonic acid groups or carboxyl groups into the main chain aromatic ring, and have proposed a process for producing a sulfonation product of an aniline copolymer by copolymerizing at least one compound selected from the group consisting of aniline, N-alkylanilines and phenylenediamines with aminobenzenesulfonic acid using an oxidizing agent in an acidic solvent and further sulfonating the resulting copolymer with a sulfonating agent (JP-A-5-178,989). However, the above process has had a problem of treatment of wasted acid because the sulfonation operation is effected in conc. sulfuric acid. Incidentally, the copolymers synthesized are all inferred to have the structures represented by the general formula (7): ##STR1## wherein each of R.sub.11 to R.sub.14 is a group selected from the group consisting of hydrogen and sulfonic acid group; R' is a group selected from the group consisting of hydrogen and alkyl groups having 1 to 4 carbon atoms; the number of the sulfonic acid group is 40 to 80% of the number of the aromatic ring; x represents any number of 0 to 1 and n is a numeral of 2 to 1,500 showing the degree of polymerization.
In addition, the present inventors have proposed a process for producing an aniline copolymer, characterized by copolymerizing at least one compound selected from the group consisting of aniline, N-alkylanilines and phenylenediamines with an alkoxy group-substituted aminobenzenesulfonic acid. Thereby omitting the sulfonation operation which causes a large amount of waste (JP-A-6-293,828). Incidentally, the copolymers synthesized are all inferred to have the structures represented by the general formula (8): ##STR2## wherein each of R.sub.15 to R.sub.22 is a group selected from the group consisting of hydrogen, alkoxy groups and sulfonic acid group; the number of the sulfonic acid group is 25 to 50% of the number of the aromatic ring; the alkoxy group and the sulfonic acid group are contained in one and the same aromatic ring; R' is a group selected from the group consisting of hydrogen and alkyl groups having 1 to 4 carbon atoms; x represents any number of 0 to 1 and n is a numeral of 2 to 1,500 which shows the degree of polymerization.
Furthermore, the present inventors have proposed a process for producing a soluble conductive polymer of the soluble aniline type by polymerizing an acidic group-substituted aniline such as a sulfonic acid group-substituted aniline, a carboxyl group-substituted aniline or the like in a solution containing a basic compound (JP-A-7-196,791 and JP-A-7-324,132). According to this process, contrary to the conventional established theory that it is difficult to polymerize alone anilines having sulfonic acid groups or carboxyl groups, it is possible to produce a high molecular weight polymer. In addition, the soluble conductive polymer obtained exhibits a high conductivity and also exhibits an excellent dissolvability in both acidic and alkaline aqueous solutions. However, when the soluble conductive polymer is separated from the by-product salt of the oxidizing agent used in the oxidative polymerization, the operation thereof has not been easy on a commercial scale because the dissolvability of the soluble conductive polymer per se is very excellent. Incidentally, the copolymers synthesized by the above-mentioned processes are inferred to have the structures represented by the general formula (9): ##STR3## wherein each of A.sub.1 to A.sub.4 is a group selected from the group consisting of sulfonic group, carboxyl group and their alkali metal salts, ammonium salts and substituted ammonium salts; each of B.sub.1 to B.sub.4 is a group selected from the group consisting of hydrogen, straight chain or branched chain alkyl groups having 1 to 4 carbon atoms; straight chain or branched chain alkoxy groups having 1 to 4 carbon atoms, acidic groups, hydroxyl group, nitro group and halogen groups; x represents any number of 0 to 1; and n represents a numeral of 2 to 5,000 which shows the degree of polymerization.
On the other hand, there have been reported a process for synthesizing a sulfonated polyaniline by electrochemically polymerizing aniline and m-aminobenzenesulfonic acid (Journal of The Chemical Society of Japan, 1985, 1124 and JP-A-02-166,165) and a process for electrochemically polymerizing aminobenzenesulfonic acid [Preprint II of the 64th Autumn Annual Convention of The Chemical Society of Japan, 706 (1992)]. However, in these processes, an inorganic salt is added as an electrolyte, and hence, there is such a problem that the operation for separating the soluble conductive polymer from the electrolyte after the polymerization is complicated and the application of the processes to the mass production on a commercial scale is very difficult.