Method for producing conductive polymer dispersion

Abstract

To provide a method for producing a conductive polymer dispersion having a low content of free anions.SOLUTION: A polymerization step of polymerizing a monomer for forming a π - conjugated conductive polymer in a reaction liquid containing at least one of an oxidizing agent and a catalyst, a polyanion, and an aqueous dispersion medium, to thereby obtain a conductive polymer dispersion liquid containing a conductive composite containing the π - conjugated conductive polymer and the polyanion, the aqueous dispersion medium, and an anion; Thereafter, a first anion purification step of separating the conductive polymer dispersion from the anion exchange resin to obtain the conductive polymer dispersion, a dispersion step of dispersing the conductive polymer dispersion at a high pressure, and a second anion purification step of bringing the conductive polymer dispersion obtained in the dispersion step into contact with an anion exchange resin, and then separating the conductive polymer dispersion from the anion exchange resin to obtain the conductive polymer dispersion.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a conductive polymer dispersion containing a π-conjugated conductive polymer and a polyanion. [Background technology]

[0002] A π-conjugated conductive polymer whose main chain is composed of a π-conjugated system forms a conductive complex by doping with a polyanion having an anionic group, and becomes dispersible in water. Patent Document 1 proposes an adhesive sheet having an adhesive layer formed from an adhesive composition obtained by mixing a conductive complex (conductive polymer complex) and an adhesive polymer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2020-529511 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 states that a low metal ion concentration in a pressure-sensitive adhesive composition is desirable from the viewpoint of reducing the formation of aggregated precipitates in the pressure-sensitive adhesive composition. Therefore, it is required that the amount of metal ions carried over from the materials used in producing the pressure-sensitive adhesive composition is small. Furthermore, regardless of the application of the pressure-sensitive adhesive composition, a conductive polymer dispersion in which a conductive complex is dispersed may also be required to have a small amount of free ions.

[0005] The present invention provides a method for producing a conductive polymer dispersion having a low content of free anions. [Means for solving the problem]

[0006] [1] A method for producing a conductive polymer dispersion, comprising: a polymerization step of polymerizing a monomer that forms a π-conjugated conductive polymer in a reaction solution containing at least one of an oxidant and a catalyst, a polyanion, and an aqueous dispersion medium to obtain a conductive polymer dispersion containing a conductive complex containing the π-conjugated conductive polymer and the polyanion, the aqueous dispersion medium, and anions; a first anion purification step of contacting the conductive polymer dispersion with an anion exchange resin and then separating the conductive polymer dispersion from the anion exchange resin; a dispersion step of dispersing the conductive polymer dispersion under high pressure; and a second anion purification step of contacting the conductive polymer dispersion obtained in the dispersion step with an anion exchange resin and then separating the conductive polymer dispersion from the anion exchange resin. [2] The method for producing a conductive polymer dispersion according to [1], wherein the content of water relative to the total mass of the aqueous dispersion medium is 70 mass % or more. [3] The method for producing a conductive polymer dispersion according to [1] or [2], wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene). [4] The method for producing a conductive polymer dispersion according to any one of [1] to [3], wherein the polyanion is polystyrene sulfonic acid. [5] The method for producing a conductive polymer dispersion according to any one of [1] to [4], wherein the oxidizing agent contains sulfate ions. [6] The method for producing a conductive polymer dispersion according to any one of [1] to [5], wherein the oxidizing agent is a persulfate. [7] The method for producing a conductive polymer dispersion according to any one of [1] to [6], wherein the oxidizing agent is sodium persulfate. [8] The method for producing a conductive polymer dispersion according to any one of [1] to [7], wherein the oxidizing agent is ammonium persulfate. [9] The method for producing a conductive polymer dispersion according to any one of [1] to [8], further comprising a multistage anion purification step, in which the conductive polymer dispersion is contacted with an anion exchange resin and then the conductive polymer dispersion is separated from the anion exchange resin, and the multistage anion purification step is carried out one or more times after the second anion purification step.

[10] The method for producing a conductive polymer dispersion according to any one of [1] to [9], wherein the conductive polymer dispersion obtained through the second anion purification step has a sulfate ion concentration of 13 ppm or less. [Effects of the Invention]

[0007] According to the present invention, a conductive polymer dispersion liquid having a low content of free anions can be produced.

[0008] This invention is believed to contribute to SDG Goal 12, "Responsible Consumption and Production."

[0009] In this specification and claims, the lower and upper limits of numerical ranges indicated with "to" are included in the numerical range. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Method for producing conductive polymer dispersion> A first aspect of the present invention is a method for producing a conductive polymer dispersion, comprising the following polymerization step, first anion purification step, dispersion step, and second anion purification step.

[0011] [Polymerization process] This step is a step of polymerizing a monomer that forms a π-conjugated conductive polymer in a reaction liquid containing at least one of an oxidant and a catalyst, a polyanion, and an aqueous dispersion medium, thereby obtaining a conductive polymer dispersion liquid that contains a conductive complex that contains the π-conjugated conductive polymer and the polyanion, the aqueous dispersion medium, and an anion.

[0012] (polyanion) A polyanion is a polymer having two or more monomer units with an anionic group in the molecule. The anionic group of the polyanion functions as a dopant for a π-conjugated conductive polymer, improving the conductivity of the π-conjugated conductive polymer. The anionic group of the polyanion is preferably a sulfo group or a carboxy group. Specific examples of polyanions include polymers having sulfo groups, such as polystyrene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyacrylic acid esters having sulfo groups, polymethacrylic acid esters having sulfo groups (for example, poly(4-sulfobutyl methacrylate, polysulfoethyl methacrylate, polymethacryloyloxybenzenesulfonic acid), poly(2-acrylamido-2-methylpropanesulfonic acid), and polyisoprene sulfonic acid; and polymers having carboxy groups, such as polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacrylic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanecarboxylic acid), and polyisoprene carboxylic acid. The polyanion may be a homopolymer formed by polymerizing a single monomer, or a copolymer formed by polymerizing two or more types of monomers. Among these polyanions, polymers having sulfo groups are preferred, and polystyrene sulfonic acid is more preferred, since they can further increase the conductivity. The weight average molecular weight of the polyanion is preferably from 10,000 to 1,000,000, and more preferably from 100,000 to 500,000.

[0013] The amount of the polyanion relative to the total mass of the reaction solution is, for example, preferably 0.1% by mass to 3.0% by mass, more preferably 0.5% by mass to 2.0% by mass, and even more preferably 1.0% by mass to 1.5% by mass. Within the above range, a conductive polymer dispersion liquid in which the conductive composite has good dispersibility can be easily obtained. In addition, the blending ratio of the polyanion and the monomer blended in the reaction liquid is reflected in the content ratio of the π-conjugated conductive polymer and the polyanion contained in the conductive composite.

[0014] The polyanion to be added to the reaction solution may be synthesized by a known method or may be a commercially available product.

[0015] (Monomers that form π-conjugated conductive polymers) The monomers to be added to the reaction solution preferably form the following π-conjugated conductive polymer. The π-conjugated conductive polymer may be an organic polymer whose main chain is composed of a π-conjugated system, and examples thereof include polypyrrole-based conductive polymers, polythiophene-based conductive polymers, polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, polyphenylene vinylene-based conductive polymers, polyaniline-based conductive polymers, polyacene-based conductive polymers, polythiophene vinylene-based conductive polymers, and copolymers thereof. From the viewpoint of stability in air, polypyrrole-based conductive polymers, polythiophenes, and polyaniline-based conductive polymers are preferred, and from the viewpoint of transparency, polythiophene-based conductive polymers are more preferred.

[0016] Polythiophene-based conductive polymers include polythiophene, poly(3-methylthiophene), poly(3-ethylthiophene), poly(3-propylthiophene), poly(3-butylthiophene), poly(3-hexylthiophene), poly(3-heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly(3-chlorothiophene), and poly(3-iodothiophene). thiophene), poly(3-cyanothiophene), poly(3-phenylthiophene), poly(3,4-dimethylthiophene), poly(3,4-dibutylthiophene), poly(3-hydroxythiophene), poly(3-methoxythiophene), poly(3-ethoxythiophene), poly(3-butoxythiophene), poly(3-hexyloxythiophene), poly(3-heptyloxythiophene), poly(3-octyloxythiophene), poly(3-decyloxythiophene), poly(3-dodecyloxythiophene) oxythiophene), poly(3-octadecyloxythiophene), poly(3,4-dihydroxythiophene), poly(3,4-dimethoxythiophene), poly(3,4-diethoxythiophene), poly(3,4-dipropoxythiophene), poly(3,4-dibutoxythiophene), poly(3,4-dihexyloxythiophene), poly(3,4-diheptyloxythiophene), poly(3,4-dioctyloxythiophene), poly(3,4-didecyloxythiophene), poly(3,4-di dodecyloxythiophene), poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), poly(3,4-butylenedioxythiophene), poly(3-methyl-4-methoxythiophene), poly(3-methyl-4-ethoxythiophene), poly(3-carboxythiophene), poly(3-methyl-4-carboxythiophene), poly(3-methyl-4-carboxyethylthiophene), and poly(3-methyl-4-carboxybutylthiophene). Examples of polypyrrole-based conductive polymers include polypyrrole, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-ethylpyrrole), poly(3-n-propylpyrrole), poly(3-butylpyrrole), poly(3-octylpyrrole), poly(3-decylpyrrole), poly(3-dodecylpyrrole), poly(3,4-dimethylpyrrole), poly(3,4-dibutylpyrrole), poly(3-carboxypyrrole), poly(3-methyl-4-carboxypyrrole), poly(3-methyl-4-carboxyethylpyrrole), poly(3-methyl-4-carboxybutylpyrrole), poly(3-hydroxypyrrole), poly(3-methoxypyrrole), poly(3-ethoxypyrrole), poly(3-butoxypyrrole), poly(3-hexyloxypyrrole), and poly(3-methyl-4-hexyloxypyrrole). Examples of polyaniline-based conductive polymers include polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-anilinesulfonic acid), and poly(3-anilinesulfonic acid). Among these π-conjugated conductive polymers, poly(3,4-ethylenedioxythiophene) is particularly preferred because of its excellent conductivity, transparency, and heat resistance. The conductive composite may contain one or more types of π-conjugated conductive polymers, i.e., the type of monomers blended into the reaction solution may be one or two or more types.

[0017] The amount of the monomer relative to the total mass of the reaction liquid is, for example, preferably 0.01% by mass to 2.0% by mass, more preferably 0.1% by mass to 1.0% by mass, and even more preferably 0.3% by mass to 0.8% by mass. Within the above range, a conductive polymer dispersion liquid in which the conductive composite has good dispersibility can be easily obtained. In addition, the blending ratio of the monomer and the polyanion blended in the reaction liquid is reflected in the content ratio of the π-conjugated conductive polymer and the polyanion contained in the conductive composite.

[0018] (aqueous dispersion medium) The dispersion medium constituting the reaction solution is preferably an aqueous dispersion medium containing water, since it easily dissolves the polyanion, ensures the polymerization reaction, and the conductive composite formed by the polymerization reaction of the π-conjugated conductive polymer and the polyanion is hydrophilic. Furthermore, the reaction solution may contain a dispersion medium other than water, as long as it does not significantly impair the effects of the present invention.

[0019] The dispersion medium other than water is preferably a water-soluble organic solvent. Here, the water-soluble organic solvent is an organic solvent that dissolves in an amount of 1 g or more in 100 g of water at 20°C, and examples thereof include alcohol-based solvents, ketone-based solvents, and ester-based solvents. The water-soluble organic solvent contained as the dispersion medium may be one type or two or more types.

[0020] The content of water relative to the total mass of the aqueous dispersion medium is preferably from 60 to 100 mass %, more preferably from 70 to 100 mass %, and even more preferably from 90 to 100 mass %. Within the above range, the dispersion stability of the conductive composite in the conductive polymer dispersion liquid is good.

[0021] (oxidizing agent, catalyst) In order to promote the oxidative polymerization reaction of the monomer, it is preferable to add an oxidizing agent to the reaction solution. The oxidizing agent is preferably a salt because it has high solubility in an aqueous dispersion medium. Examples of such oxidizing agents include those containing sulfate ions, sodium ions, ammonium ions, and potassium ions.

[0022] The oxidizing agent is preferably a polymerization initiator. The polymerization initiator is preferably a radical polymerization initiator, more preferably a persulfate, because it exhibits excellent polymerizability. The persulfate added to the reaction solution decomposes to function as a radical polymerization initiator and may also generate free anions in the reaction solution.

[0023] Examples of persulfates include ammonium persulfate, sodium persulfate, potassium persulfate, etc. The anions constituting these persulfates should be purified in a subsequent anion purification step.

[0024] The amount of the oxidizing agent relative to the total mass of the reaction liquid is, for example, preferably 0.10% by mass or more and 1.50% by mass or less, more preferably 0.25% by mass or more and 1.25% by mass or less, and even more preferably 0.40% by mass or more and 1.00% by mass or less.

[0025] It is preferable to add a catalyst such as a transition metal compound, such as ferric chloride, ferric sulfate, ferric nitrate, or cupric chloride, to the reaction liquid together with the oxidizing agent. The amount of catalyst to be added is adjusted appropriately according to the amount of oxidizing agent to be added. Since the anions constituting the catalyst are to be purified in the subsequent anion purification step, it is preferable to keep the amount to the minimum necessary.

[0026] The oxidizing agent is preferably added last to the reaction solution after all other reaction components have been mixed, to initiate polymerization. A radical polymerization initiator, which is a type of oxidizing agent, is preferably dissolved in a small amount of water and added to the reaction solution. The addition method may involve adding the entire amount all at once, or adding it stepwise in stages. It is preferable to add a certain amount slowly over a predetermined period of time (for example, 2 to 4 hours).

[0027] The reaction temperature in the reaction solution can be, for example, 20 to 30°C. At the reaction temperature, the polymerization reaction is usually completed in about 4 to 12 hours. The completion of the polymerization reaction can be determined by measuring the amount of unreacted monomer in the reaction solution using known methods such as chromatography.

[0028] (Conductive composite) The conductive complex containing a π-conjugated conductive polymer and a polyanion is formed by spontaneous doping of the polyanion with the π-conjugated conductive polymer formed by polymerization of the monomer in the reaction solution. In water, the π-conjugated conductive polymer is positively charged and the polyanion is negatively charged, and it is believed that the two form the complex mainly through electrostatic interaction.

[0029] In the polyanion constituting the conductive composite, only a portion of the anionic groups is doped into the π-conjugated conductive polymer, and there are excess anionic groups that are not involved in the doping. Because the excess anionic groups are hydrophilic groups, the conductive composite has water dispersibility. When the number of all anionic groups in the polyanion is taken as 100 mol %, the excess anionic groups are preferably 30 mol % or more and 90 mol % or less, and more preferably 45 mol % or more and 75 mol % or less.

[0030] The content of the polyanion in the conductive composite is, for example, preferably in the range of 1 part by mass to 1,000 parts by mass, more preferably 10 parts by mass to 700 parts by mass, and even more preferably 100 parts by mass to 500 parts by mass, relative to 100 parts by mass of the π-conjugated conductive polymer. If the content of the polyanion is equal to or greater than the lower limit, the doping effect on the π-conjugated conductive polymer tends to be stronger, resulting in higher conductivity. On the other hand, if the content of the polyanion is equal to or less than the upper limit, the content of the π-conjugated conductive polymer is sufficient, thereby ensuring sufficient conductivity.

[0031] The upper limit of the content of the conductive complex relative to the total mass of the conductive polymer dispersion obtained in the polymerization step is preferably 5.0 mass% or less, more preferably 4.0 mass% or less, even more preferably 3.0 mass% or less, and most preferably 2.0 mass% or less. Here, the lower limit is not particularly limited and can be set appropriately depending on the application of the conductive polymer dispersion, and may be, for example, 0.1 mass% or more. When the content is equal to or less than the upper limit, the dispersibility of the conductive composite in the conductive polymer dispersion can be improved, and the amount of loss of the conductive composite in the subsequent purification step can be reduced.

[0032] The conductive polymer dispersion obtained in the polymerization process usually contains free anions derived from the oxidizing agent, catalyst, or other materials, which are removed in a series of subsequent purification steps.

[0033] [First anion purification process] This step involves contacting the conductive polymer dispersion obtained in the previous polymerization step with an anion exchange resin, and then separating the conductive polymer dispersion from the anion exchange resin.

[0034] The type of anion exchange resin to be used is not particularly limited, but is preferably one that can adsorb free anions and replace them with hydroxy ions in the aqueous dispersion medium. Furthermore, the anion exchange resin is an insoluble carrier that carries anion exchange functional groups, and the carrier is preferably porous, with micropores that are large enough to allow polymers to penetrate but large enough to allow free anions and low-molecular-weight molecules to penetrate. A suitable anion exchange resin is, for example, Duolite A368MS (manufactured by Sumika Chemtex Co., Ltd.), which is used in the examples described below.

[0035] When the treatment with an anion exchange resin is carried out in this step, a treatment with a cation exchange resin may be carried out in parallel. By bringing the conductive polymer dispersion into contact with the cation exchange resin, free cations derived from the oxidizing agent, catalyst, etc. can be adsorbed and removed from the conductive polymer dispersion.

[0036] The type of cation exchange resin used is not particularly limited, but is preferably one that can adsorb free cations and replace them with protons in an aqueous dispersion medium. The cation exchange resin preferably has cation exchange functional groups held on an insoluble carrier, the carrier being porous, and the size of the micropores in the carrier is such that polymers have difficulty penetrating but free cations and low-molecular-weight molecules can easily penetrate. A suitable cation exchange resin is, for example, Duolite C255LFH (manufactured by Sumika Chemtex Co., Ltd.), which is used in the examples described below.

[0037] The method for contacting the conductive polymer dispersion with the ion exchange resin is not particularly limited, and may be a batch method, a column method, or other method. In the examples described below, a batch method was used. In the case of a batch method, stirring is preferred to increase the efficiency of contact with the ion exchange resin.

[0038] The amount of ion exchange resin to be brought into contact with the conductive polymer dispersion is preferably set to a sufficient amount relative to the expected amount of free ions. The specific amount is not particularly limited, and can be appropriately set by a general engineer in this technical field based on experience.

[0039] The time for contacting the conductive polymer dispersion with the ion exchange resin is preferably set to a sufficient time relative to the expected amount of free ions. The specific time is not particularly limited, and can be appropriately set by a general engineer in this technical field based on experience. For example, a few minutes to a few hours may be used as a guideline for a batch method, and a few tens of seconds to a few tens of minutes may be used as a guideline for a column method.

[0040] After the above contact, the method for separating the ion exchange resin to obtain a conductive polymer dispersion is not particularly limited, and can be carried out appropriately depending on the contact method. For example, in the case of a batch method, the ion exchange resin can be filtered through filter paper or a filter, and a conductive polymer dispersion from which the ion exchange resin has been removed can be obtained as a filtrate. For example, in the case of a column method, the conductive polymer dispersion from which free ions have been removed can be obtained by passing the dispersion through a column filled with an ion exchange resin.

[0041] According to the experience of the present inventors, free anions still remain in the conductive polymer dispersion obtained after the first anion purification step. Although the reason for this is not entirely clear, it is believed that one factor is that the anions adsorbed to the conductive composite are released into the aqueous dispersion medium after the first anion purification step. For this reason, in the present invention, a second anion purification step is further performed. However, prior to this, a dispersion step is performed in which the conductive polymer dispersion obtained in the first anion purification step is dispersed at high pressure using a high-pressure homogenizer or the like.

[0042] [Dispersion process] This step is a step in which a dispersion treatment is carried out under high pressure on the conductive polymer dispersion liquid that has been separated from the anion exchange resin after the first anion purification step. Here, "high pressure" refers to a high pressure that cannot be achieved by manual stirring. Suitable pressures include, for example, 10 to 350 MPa (100 to 3500 bar). Within this range, other examples include ranges of 50 to 310 MPa and 100 to 310 MPa. 3500 bar is approximately 50,763 psi. When pressure is applied in any direction in a container or flow channel, the conductive polymer dispersion collides with each other or passes through narrow gaps, generating turbulence and shear forces, which result in the finer particles of the conductive composite and improve the dispersibility of the conductive composite. During this process, it is thought that the agglomerates of the conductive composite are broken down, and free anions such as sulfate ions that were caught in the agglomerates are released into the conductive polymer dispersion.

[0043] As the apparatus for carrying out the dispersion treatment, a commercially available high-pressure homogenizer can be used. The dispersion treatment time may be, for example, several minutes to several tens of minutes. The temperature of the conductive polymer dispersion during the dispersion treatment is, for example, 4 to 30°C. One indicator of the completion of the dispersion treatment is whether the content of free anions (e.g., sulfate ions) before the dispersion treatment has increased after the dispersion treatment. One of the purposes of this step is to liberate the anions adsorbed on the conductive composite.

[0044] [Second anion purification process] This step involves bringing the conductive polymer dispersion obtained in the previous dispersion step into contact with an anion exchange resin, and then separating the conductive polymer dispersion from the anion exchange resin.

[0045] The type of anion exchange resin used is not particularly limited, and may be the same type as the anion exchange resin used in the first anion purification step, or may be a different type. The anion exchange resin used in the first anion purification step itself adsorbs anions during use, and its anion adsorption capacity may be reduced, so it is not recommended to reuse it as is. For this reason, it is preferable to use a new anion exchange resin or an anion exchange resin whose ion adsorption capacity has been restored through a known regeneration process.

[0046] In the second anion purification step, similarly to the first anion purification step, treatment with a cation exchange resin may be carried out in parallel with treatment with an anion exchange resin.

[0047] In the second anion purification step, as in the first anion purification step, the method for contacting the conductive polymer dispersion with the ion exchange resin is not particularly limited, and may be a batch method, a column method, or any other method.

[0048] In the second anion purification step, as in the first anion purification step, it is preferable to set the amount of ion exchange resin to be brought into contact with the conductive polymer dispersion to a sufficient amount relative to the expected amount of free ions.

[0049] In the second anion purification step, as in the first anion purification step, it is preferable to set the time for contacting the conductive polymer dispersion with the ion exchange resin to a time sufficient for the expected amount of free ions.

[0050] In the second anion purification step, as in the first anion purification step, the method for separating the ion exchange resin after the above contact to obtain a conductive polymer dispersion is not particularly limited, and may be carried out appropriately depending on the contact method.

[0051] According to the experience of the present inventors, free anions may still be present in the conductive polymer dispersion obtained by carrying out the second anion purification step. If a higher degree of purification is required, a further anion purification step may be carried out.

[0052] [Multi-stage anion purification process] This step is a step of carrying out a further anion purification step after the second anion purification step. The specific treatment of the further anion purification step is the same as that of the second anion purification step, so the overlapping explanation will be omitted. After the second anion purification step, the number of times the further anion purification step is repeated is not particularly limited, and the step may be repeated once or twice or more as desired.

[0053] In the conductive polymer dispersion obtained through the above anion purification process, free anions have been sufficiently removed, and for example, a conductive polymer dispersion with a sulfate ion concentration of 13 ppm or less can be obtained.

[0054] [Measurement of anion concentration] The concentration of free ions contained in the conductive polymer dispersion can be measured, for example, in ppm units based on the mass relative to the total mass of the conductive polymer dispersion to be measured. Specifically, the measurement can be performed by a known method using ion chromatography. It is preferable to prepare a calibration curve in advance using standard samples with known ion concentrations. For example, the ion concentration can be calculated by measuring using an LC-2000 (manufactured by JASCO Corporation) as a measuring device, using a Shodex IC SI-90 4E column and an electric conductivity detector. [Example]

[0055] (Production Example 1) Production of polystyrene sulfonic acid 206 g of sodium styrenesulfonate was dissolved in 1000 ml of ion-exchanged water, and while stirring at 80°C, 1.14 g of an oxidizing agent solution of ammonium persulfate, which had been dissolved in 10 ml of water in advance, was added dropwise over 20 minutes, and the solution was stirred for 12 hours. To the resulting sodium polystyrene sulfonate solution, 1000 ml of sulfuric acid diluted to 10% by mass was added, and approximately 1000 ml of the solvent from the resulting polystyrene sulfonic acid solution was removed by ultrafiltration. Next, 2000 ml of ion-exchanged water was added to the remaining solution, and approximately 2000 ml of the solvent was removed by ultrafiltration, and the polystyrene sulfonic acid was washed with water. This water washing procedure was repeated three times. Water in the obtained solution was removed under reduced pressure to obtain colorless solid polystyrene sulfonic acid (PSS). 10 g of this polystyrene sulfonic acid was dissolved in 90 g of ion-exchanged water to obtain a 10 mass % aqueous polystyrene sulfonic acid solution.

[0056] The weight-average molecular weight (Mw) of the polystyrene sulfonic acid aqueous solution obtained above was measured by gel permeation chromatography (GPC) using pullulan of known weight-average molecular weight as the standard substance, and the weight-average molecular weight was found to be 200,000.

[0057] The weight-average molecular weight was measured using a Prominence high-performance liquid chromatograph manufactured by Shimadzu Corporation, using 0.1% aqueous NaNO3 solution as the solvent, a Shodex OHpack SB-806M HQ column, and a RID-20A detector. The solvent temperature was set to 40°C, the flow rate was set to 0.6 ml / min, the PSS concentration in the sample was set to 0.1% by mass, and 100 μl of the sample filtered through a membrane filter with a pore size of 0.2 μm was injected, and the measurement was performed using the Lab Solutions analysis software (Shimadzu Corporation).

[0058] Example 1: Preparation of conductive polymer dispersion 5.7 g of 3,4-ethylenedioxythiophene (EDOT), 145.3 g of polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, and 773.0 g of ion-exchanged water were mixed at 25°C. The resulting mixed solution was kept at 25°C and 19.2 g of a 6% aqueous solution of ferric sulfate was added while stirring. Next, 48.3 g of an 11% aqueous solution of sodium persulfate was added, and the resulting reaction solution was reacted with stirring for 8 hours. Through the above reaction, a conductive polymer dispersion A was obtained, which contained a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, which are π-conjugated conductive polymers, and water, which is a dispersion medium.

[0059] When the obtained conductive polymer dispersion A was analyzed by GPC, the amount of unpolymerized EDOT was below the detection limit.

[0060] To conductive polymer dispersion A, 66.0 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Co., Ltd.) and 66.0 g of Duolite A368MS (an anion exchange resin manufactured by Sumika Chemtex Co., Ltd.) were added, and the mixture was filtered to remove the ion exchange resin. The resulting filtrate was dispersed using a high-pressure homogenizer with strong shear force, and then 66.0 g of Duolite C255LFH and 66.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. 850 g of conductive polymer dispersion from which the oxidant and catalyst had been removed was obtained, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 1.4 mass%.

[0061] Example 2 To the conductive polymer dispersion A obtained in Example 1, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. The resulting filtrate was dispersed using a high-pressure homogenizer with strong shear force, and then 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. To the resulting filtrate, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. 850 g of a conductive polymer dispersion from which the oxidizing agent and catalyst had been removed was obtained, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 1.4 mass%.

[0062] (Comparative Example 1) To the conductive polymer dispersion A obtained in Example 1, 66.0 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Co., Ltd.) and 66.0 g of Duolite A368MS (an anion exchange resin manufactured by Sumika Chemtex Co., Ltd.) were added, and the mixture was filtered to remove the ion exchange resin. To the resulting filtrate, 66.0 g of Duolite C255LFH and 66.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin, yielding 850 g of a conductive polymer dispersion from which the oxidizing agent and catalyst had been removed, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 1.4 mass%.

[0063] (Comparative Example 2) To the conductive polymer dispersion A obtained in Example 1, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. To the resulting filtrate, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. To the resulting filtrate, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. 850 g of a conductive polymer dispersion from which the oxidizing agent and catalyst had been removed was obtained, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 1.4 mass%.

[0064] The amount of sulfate ions (ppm) contained in the conductive polymer dispersions finally obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was measured by the above-mentioned method using ion chromatography. The results are shown in Table 1.

[0065] [Table 1]

[0066] Example 3: Preparation of conductive polymer dispersion 5.7 g of 3,4-ethylenedioxythiophene (EDOT), 145.3 g of polystyrene sulfonic acid (10% by mass aqueous solution) of Production Example 1, and 773.0 g of ion-exchanged water were mixed at 25°C. The resulting mixed solution was kept at 25°C and 19.2 g of a 6% aqueous solution of ferric sulfate was added while stirring. Next, 48.3 g of an 11% aqueous solution of ammonium persulfate was added, and the resulting reaction solution was stirred for 8 hours to react. Through the above reaction, a conductive polymer dispersion B was obtained, which contained a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, which are π-conjugated conductive polymers, and water, which is a dispersion medium.

[0067] When the obtained conductive polymer dispersion B was analyzed by GPC, the amount of unpolymerized EDOT was below the detection limit.

[0068] To conductive polymer dispersion B, 66.0 g of Duolite C255LFH and 66.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. The resulting filtrate was dispersed using a high-pressure homogenizer with strong shear force, and then 66.0 g of Duolite C255LFH and 66.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. 850 g of conductive polymer dispersion from which the oxidizing agent and catalyst had been removed was obtained, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 1.4 mass%.

[0069] Example 4 To the conductive polymer dispersion B obtained in Example 3, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. The resulting filtrate was dispersed using a high-pressure homogenizer with strong shear force, and then 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. To the resulting filtrate, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. 850 g of a conductive polymer dispersion from which the oxidizing agent and catalyst had been removed was obtained, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 1.4 mass%.

[0070] (Comparative Example 3) To the conductive polymer dispersion B obtained in Example 3, 66.0 g of Duolite C255LFH and 66.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. To the resulting filtrate, 66.0 g of Duolite C255LFH and 66.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin, yielding 850 g of a conductive polymer dispersion from which the oxidizing agent and catalyst had been removed, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 1.4 mass%.

[0071] Comparative Example 4 To the conductive polymer dispersion B obtained in Example 3, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. To the resulting filtrate, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. To the resulting filtrate, 44.0 g of Duolite C255LFH and 44.0 g of Duolite A368MS were added, and the mixture was filtered to remove the ion exchange resin. 850 g of a conductive polymer dispersion from which the oxidizing agent and catalyst had been removed was obtained, and the solids content (non-volatile components) was measured. The solids content of the resulting conductive polymer dispersion was 1.4 mass%.

[0072] The amount of sulfate ions (ppm) contained in the conductive polymer dispersions finally obtained in Examples 3 and 4 and Comparative Examples 3 and 4 was measured by the method using ion chromatography described above. The results are shown in Table 2.

[0073] [Table 2]

[0074] From the above test results, it is clear that the manufacturing methods of Examples 1 to 4 according to the present invention, which include a dispersion step between the first anion purification step and the second anion purification step, can produce conductive polymer dispersions with a significantly lower content of free anions compared to Comparative Examples 1 to 4.

Claims

1. A method for producing a π-conjugated conductive polymer by polymerizing a monomer that forms a π-conjugated conductive polymer in a reaction solution containing at least one of an oxidizing agent and a catalyst, a polyanion, and an aqueous dispersion medium, a polymerization step of obtaining a conductive polymer dispersion liquid containing a conductive complex containing the π-conjugated conductive polymer and the polyanion, the aqueous dispersion medium, and an anion; a first anion purification step of contacting the conductive polymer dispersion with an anion exchange resin and then separating the conductive polymer dispersion from the anion exchange resin; a dispersing step of dispersing the conductive polymer dispersion under high pressure; a second anion purification step of contacting the conductive polymer dispersion obtained in the dispersion step with an anion exchange resin, and then separating the conductive polymer dispersion from the anion exchange resin.

2. The method for producing a conductive polymer dispersion according to claim 1 , wherein the content of water relative to the total mass of the aqueous dispersion medium is 70 mass % or more.

3. 3. The method for producing a conductive polymer dispersion according to claim 2, wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene).

4. The method for producing a conductive polymer dispersion according to claim 3 , wherein the polyanion is polystyrene sulfonic acid.

5. The method for producing a conductive polymer dispersion according to claim 4 , wherein the oxidizing agent contains sulfate ions.

6. The method for producing a conductive polymer dispersion according to claim 4 , wherein the oxidizing agent is a persulfate.

7. The method for producing a conductive polymer dispersion according to claim 4 , wherein the oxidizing agent is sodium persulfate.

8. The method for producing a conductive polymer dispersion according to claim 4 , wherein the oxidizing agent is ammonium persulfate.

9. an anion purification step of contacting the conductive polymer dispersion with an anion exchange resin, and then separating the conductive polymer dispersion from the anion exchange resin; The method for producing a conductive polymer dispersion according to claim 4 , further comprising a multistage anion purification step being carried out one or more times after the second anion purification step.

10. 2. The method for producing a conductive polymer dispersion according to claim 1, wherein the conductive polymer dispersion obtained through the second anion purification step has a sulfate ion concentration of 13 ppm or less.

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