Aqueous dispersion containing polyamic acid / carbon nanotube

Abstract

Provided is an aqueous dispersion containing a polyamic acid / carbon nanotube, the aqueous dispersion comprising an aqueous solvent, a polyamic acid, and a carbon nanotube, wherein: the content of the polyamic acid in the aqueous dispersion is 2 mass% or more; when the aqueous dispersion is stored at 25 °C for 45 days, the viscosity ratio VR_45 of a viscosity after 45 days of storage to a viscosity at the start of storage is 1.2 or less, as calculated by the following expression (1); and when the aqueous dispersion is stored at 25 °C for 45 days, the viscosity change amount VC_45 between a viscosity after 45 days of storage and a viscosity at the start of storage is 200 cps or less, as calculated by the following expression (2).　(1): viscosity ratio VR_45=(viscosity V45 at 25 °C after 45 days of storage) / (viscosity VIni at 25 °C at start of storage) (2): viscosity change amount VC_45=|(viscosity V45 at 25 °C after 45 days of storage)−(viscosity VIni at 25 °C at start of storage)|

Description

Polyamic acid / carbon nanotube-containing aqueous dispersion

[0001] The present invention relates to a polyamic acid / carbon nanotube-containing aqueous dispersion having excellent long-term storage stability.

[0002] Carbon materials such as carbon blacks, fullerenes, graphene, and carbon nanotubes are used in a wide range of fields, including electronics and energy, due to their electrical properties and thermal conductivity. In particular, carbon nanotubes are tubular carbons with a diameter of 1 μm or less, and are expected to be used in a variety of applications due to their high electrical conductivity, tensile strength, heat resistance, and other properties based on their unique structure.

[0003] On the other hand, carbon nanotubes are obtained as entangled aggregates (also called bundles), and because the mutual cohesive forces (van der Waals forces) cause them to form bundles or ropes, and because their atomically smooth surfaces reduce their affinity for solvents, they are difficult to disperse in both polar and nonpolar solvents. For this reason, attempts have been made to disperse carbon nanotubes well in order to apply them to various applications.

[0004] For example, Patent Document 1 discloses a fine carbon dispersion composition containing a dispersant for fine carbon, which contains a polyimide precursor and a basic compound having a pKa of 7.5 or more and 0.7 times or more equivalent to the carboxyl group of the polyimide precursor, fine carbon such as carbon nanotubes, and a polar solvent.

[0005] International Publication No. 2013 / 147087

[0006] However, although conventional methods have been able to disperse fine carbon such as carbon nanotubes in polar solvents, the resulting dispersion compositions have not necessarily had sufficient long-term storage stability. The present invention has been made in view of the conventional problems, and an object of the present invention is to provide a polyamic acid / carbon nanotube-containing aqueous dispersion liquid having excellent long-term storage stability.

[0007] In order to solve the above problem, the present inventors have conducted extensive research and found that when a composition is stored at 25°C for 45 days, the viscosity ratio V Ｒ＿４５ and the viscosity change amount V Ｃ＿４５ Furthermore, the present inventors have conducted extensive research and have found that the above-mentioned problems can be solved by using a polyamic acid / carbon nanotube-containing aqueous dispersion in which the ratio of the aromatic diamine-derived units and / or the aromatic diamine-derived units in which two amine structures are located at the meta positions of one aromatic ring in a polyamic acid that constitutes the polyamic acid / carbon nanotube-containing aqueous dispersion is 50 mol % or more based on the total molar amount of the units derived from the diamine component.

[0008] That is, the present invention provides the following items [1] to

[13] : [1] A polyamic acid / carbon nanotube-containing aqueous dispersion comprising an aqueous solvent, a polyamic acid, and carbon nanotubes, wherein the content of the polyamic acid in the aqueous dispersion is 2 mass % or more, and the aqueous dispersion is stored at 25°C for 45 days, and the viscosity ratio V after storage for 45 days to the viscosity at the start of storage is calculated by the following formula (1): Ｒ＿４５ The aqueous dispersion is stored at 25° C. for 45 days, and the viscosity change V after 45 days of storage relative to the start of storage is calculated by the following formula (2): Ｃ＿４５ A polyamic acid / carbon nanotube-containing aqueous dispersion having a viscosity ratio V of 200 cps or less. Ｒ＿４５ = (Viscosity V of the aqueous dispersion at 25°C after storage for 45 days) ４５ ) / (Viscosity V of the aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) (1) Viscosity change amount V Ｃ＿４５ = | (Viscosity V of the aqueous dispersion at 25 ° C. after storage for 45 days ４５ ) - (Viscosity V of the aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) | (2)

[0009] [2] A polyamic acid / carbon nanotube-containing aqueous dispersion comprising an aqueous solvent, a polyamic acid, and carbon nanotubes, wherein the polyamic acid contains units derived from a tetracarboxylic acid component and units derived from a diamine component, and the polyamic acid contains, as the units derived from the diamine component, units derived from an aliphatic diamine and / or units derived from an aromatic diamine in which two amine structures are located at meta positions of one aromatic ring, in a proportion of 50 mol % or more based on the total molar amount of the units derived from the diamine component.

[0010] [3] The polyamic acid / carbon nanotube-containing aqueous dispersion according to [1] or [2], further containing a proton-accepting nitrogen-containing compound.

[0011] [4] The polyamic acid / carbon nanotube-containing aqueous dispersion according to any one of [1] to [3], wherein the carbon nanotubes are single-walled carbon nanotubes.

[0012] [5] The polyamic acid / carbon nanotube-containing aqueous dispersion according to any one of [1] to [4], wherein the content of the carbon nanotubes in the aqueous dispersion is 0.4 mass % or more.

[0013] [6] The polyamic acid / carbon nanotube-containing aqueous dispersion according to any one of [1] to [5], wherein the aqueous solvent contains water.

[0014] [7] A binder composition for an electrical storage device, comprising the polyamic acid / carbon nanotube-containing aqueous dispersion according to any one of [1] to [6].

[0015] [8] A slurry for an electrode containing the binder composition for a storage battery device according to [7] and an active material.

[0016] [9] An electrode for an electricity storage device, obtained by using the electrode slurry according to [8].

[0017]

[10] An electric storage device for an electric storage device, comprising the electrode according to [9].

[0018]

[11] An electromagnetic wave shielding composition comprising the polyamic acid / carbon nanotube-containing aqueous dispersion according to any one of [1] to [6].

[0019]

[12] An electromagnetic wave shielding coating film obtained by using the electromagnetic wave shielding composition according to

[11] .

[0020]

[13] An electromagnetic wave shielding laminate comprising the electromagnetic wave shielding coating film according to

[12] and a substrate.

[0021] According to the present invention, it is possible to provide a polyamic acid / carbon nanotube-containing aqueous dispersion that has excellent long-term storage stability (for example, stability when stored for 90 days or more, or when stored for 180 days or more). Furthermore, according to the present invention, it is possible to provide a binder composition for an electrical storage device, an electrode slurry, an electrode, and an electrical storage device that use such a polyamic acid / carbon nanotube-containing aqueous dispersion. Furthermore, according to the present invention, it is also possible to provide an electromagnetic wave shielding composition, an electromagnetic wave shielding coating film, and an electromagnetic wave shielding laminate that are obtained using such a polyamic acid / carbon nanotube-containing aqueous dispersion and are suitable for use in electromagnetic wave shielding.

[0022] <Polyamic Acid / Carbon Nanotube-Containing Aqueous Dispersion> The polyamic acid / carbon nanotube-containing aqueous dispersion of the present invention comprises an aqueous solvent, polyamic acid, and carbon nanotubes, wherein the content of the polyamic acid in the aqueous dispersion is 2 mass % or more, and the aqueous dispersion is stored at 25°C for 45 days, and the viscosity ratio V after storage for 45 days to the viscosity at the start of storage is calculated by the following formula (1): Ｒ＿４５ The aqueous dispersion is stored at 25° C. for 45 days, and the viscosity change V after 45 days of storage relative to the start of storage is calculated by the following formula (2): Ｃ＿４５ The aqueous dispersion containing polyamic acid / carbon nanotubes has a viscosity ratio V of 200 cps or less. Ｒ＿４５ = (Viscosity V of the aqueous dispersion at 25°C after storage for 45 days) ４５ ) / (Viscosity V of the aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) (1) Viscosity change amount VＣ＿４５ = | (Viscosity V of the aqueous dispersion at 25 ° C. after storage for 45 days ４５ ) - (Viscosity V of the aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) | (2)

[0023] Examples of the aqueous solvent include water and water-miscible organic solvents, and may be a mixed solvent of water and a water-miscible organic solvent. Examples of the water-miscible organic solvent include lower alcohols such as methanol, ethanol, propanol, and butanol, ketones such as acetone, dimethyl ketone, and methyl ethyl ketone, and ethers such as diethyl ether and dipropyl ether. These water-miscible organic solvents may be mixed with water alone, or two or more may be mixed with water in combination. From the viewpoint of dispersibility of carbon nanotubes, the aqueous solvent preferably contains at least water, more preferably contains at least 50% by mass or more of water, even more preferably contains 70% by mass or more of water, and particularly preferably contains only water.

[0024] Examples of carbon nanotubes (CNTs) include vapor-grown carbon fibers, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs). Among these, single-walled carbon nanotubes (SWCNTs) are preferred because they can impart higher electrical conductivity to the resulting electrodes when the polyamic acid / carbon nanotube-containing aqueous dispersion of the present invention (hereinafter referred to as "polyamic acid / CNT aqueous dispersion") is used as a binder composition for an electrical storage device.

[0025] The method for producing carbon nanotubes is not particularly limited, and any conventionally known production method can be used, such as a thermal decomposition method using a catalyst, an arc discharge method, a laser evaporation method, and a CVD method such as a HiPco method or a CoMoCAT method. In addition, commercially available single-walled carbon nanotubes and multi-walled carbon nanotubes can also be used.

[0026] The carbon nanotube content in the polyamic acid / CNT aqueous dispersion of the present invention is preferably 0.4% by mass or more, more preferably 0.6% by mass or more, even more preferably 0.8% by mass or more, and even more preferably 1.0% by mass or more, with the upper limit being preferably 3.0% by mass or less, more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, and particularly preferably 1.2% by mass or less. According to the polyamic acid / CNT aqueous dispersion of the present invention, even when the carbon nanotube content is set to such a relatively high level, the carbon nanotubes can be well dispersed and excellent long-term storage stability can be achieved. In particular, while conventional dispersions have had difficulty dispersing the carbon nanotubes or exhibited insufficient storage stability when the carbon nanotube content was set to such a relatively high level, the present invention effectively solves these problems.

[0027] The polyamic acid used in the present invention is obtained by reacting a tetracarboxylic acid component with a diamine component to form an amide bond (-CONH-). Therefore, the polyamic acid used in the present invention has units derived from the tetracarboxylic acid component and units derived from the diamine component. The polyamic acid preferably contains a repeating unit represented by the following formula (3), and the content of the repeating unit represented by the following formula (3) is preferably 50 mol % or more, more preferably 75 mol % or more, and even more preferably 90 mol % or more. In the above formula (3), A is one or more tetravalent groups selected from tetracarboxylic acid components by removing a carboxyl group, and B is one or more divalent groups selected from diamine components by removing an amino group.

[0028] Examples of the tetracarboxylic acid component include aromatic tetracarboxylic acid dianhydrides and aliphatic tetracarboxylic acid dianhydrides.

[0029] As the aromatic tetracarboxylic dianhydride, a tetracarboxylic dianhydride having an aromatic ring can be suitably used. Specific examples of the aromatic tetracarboxylic dianhydride include 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), pyromellitic dianhydride (PMDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride (ODPA), diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride, and bis(3,4-dicarboxyphenyl)sulfonyl ether. dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (also known as 4,4'-(hexafluoroisopropylidene)diphthalic anhydride), 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4 1,4-bis(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, p-phenylenebis(trimellitic acid monoester acid anhydride), p-biphenylenebis(trimellitic acid monoester acid anhydride), m-terphenyl-3,4,3',4'-tetracarboxylic acid dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic acid dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, and 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride. These may be used alone or in combination of two or more.

[0030] As the aliphatic tetracarboxylic acid dianhydride, an alicyclic tetracarboxylic acid dianhydride (a tetracarboxylic acid dianhydride having an alicyclic structure and no aromatic ring) can be suitably used. Specific examples of the alicyclic tetracarboxylic acid dianhydride include (1R,2S,4S,5R)-cyclohexanetetracarboxylic acid dianhydride, (1S,2R,4S,5R)-cyclohexanetetracarboxylic acid dianhydride, (1S,2S,4R,5R)-cyclohexanetetracarboxylic acid dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-tetralin-1,2-dicarboxylic acid anhydride, tetracarboxylic acid dian ... Hydrofuran-2,3,4,5-tetracarboxylic acid dianhydride, bicyclo-3,3',4,4'-tetracarboxylic acid dianhydride, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,4-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,2,3,4-cyclohexanetetracarboxylic acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, pentacyclo[8.2.1.1] ４，７ .0 ２，９ .0 ３，８ ]tetradecane-5,6,11,12-tetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, cyclohex-1-ene-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, etc. These may be used alone or in combination of two or more.

[0031] In the present invention, from the viewpoint of further improving the dispersibility of carbon nanotubes in the polyamic acid / CNT aqueous dispersion of the present invention, it is preferable to use at least an aromatic tetracarboxylic acid dianhydride as the tetracarboxylic acid component, and the proportion of units derived from the aromatic tetracarboxylic acid dianhydride is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 90 mol % or more, and particularly preferably 100 mol %, based on the total molar amount of units derived from the tetracarboxylic acid component contained in the polyamic acid. Among aromatic tetracarboxylic acid dianhydrides, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and 4,4'-oxydiphthalic dianhydride (ODPA) are preferred.

[0032] Examples of the diamine component include aromatic diamines having an aromatic group and aliphatic diamines having no aromatic ring.

[0033] Examples of aromatic diamines include 4,4'-diaminodiphenyl ether (ODA), 2,2'-dimethylbenzidine, 4,4'-diaminodiphenylmethane, 4,4'-diamino-1,2-diphenylethane, p-phenylenediamine (PPD), m-phenylenediamine (MPD), 2,4-diaminotoluene, 3,5-diaminobenzoic acid (3,5-DABA), 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4- Examples of suitable bis(4-aminophenoxy)phenyl propane include m-xylylenediamine, p-xylylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-methylenebis(2,6-xylidine), α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, 2,2'-dimethyl-4,4'-aminobiphenyl, 3,3'-dimethyl-4,4'-aminobiphenyl, 2,2'-ethylenedianiline, and 4,4'-diaminobenzanilide. These may be used alone or in combination of two or more.

[0034] Examples of the aliphatic diamine include linear and branched aliphatic diamines not containing an alicyclic structure, such as diaminobutane, diaminopentane, diaminohexane, diaminoheptane, diaminooctane, diaminononane, diaminodecane, diaminoundecane, and diaminododecane; 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-propylcyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-butylcyclohexane, 1,4-diamino-2-tert-butylcyclohexane, and 1,2-diaminocyclohexane. alicyclic diamines having an alicyclic structure such as cyclohexane, 1,3-diaminocyclobutane, 1,4-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, diaminobicycloheptane, diaminomethylbicycloheptane, diaminooxybicycloheptane, diaminomethyloxybicycloheptane, isophoronediamine, diaminotricyclodecane, diaminomethyltricyclodecane, bis(aminocyclohexyl)methane, bis(aminocyclohexyl)isopropylidene, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, and 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane. These can be used alone or in combination of two or more.

[0035] Among these, from the viewpoint of further enhancing the long-term storage stability of the polyamic acid / CNT aqueous dispersion of the present invention, it is preferable to use at least an aliphatic diamine or an aromatic diamine in which two amine structures are located at the meta-position of a single aromatic ring, and it is more preferable to use an aliphatic diamine. Among aliphatic diamines, linear and branched aliphatic diamines that do not contain an alicyclic structure are preferred, linear aliphatic diamines that do not contain an alicyclic structure are more preferred, and 1,10-diaminodecane (DMD) is more preferred. Furthermore, an aromatic diamine in which two amine structures are located at the meta-position of a single aromatic ring is a diamine compound in which two amine structures (amino groups or groups containing amino groups) are bonded to a single aromatic ring, and the other amine structure is located at the meta-position relative to one of the amine structures. Examples of such compounds include 2,4-diaminotoluene, m-phenylenediamine (MPD), and m-xylylenediamine, with m-phenylenediamine (MPD) being preferred. In addition, the aromatic diamine in which two amine structures are located at the meta position of one aromatic ring is preferably one in which the aromatic ring having the two amine structures does not have any polar substituents other than the amine structures.

[0036] The polyamic acid used in the present invention preferably has a total content of aliphatic diamine-derived units and aromatic diamine-derived units in which two amine structures are located at meta positions on one aromatic ring of 50 mol% or more, preferably 60 to 95 mol%, and more preferably 65 to 90 mol%, based on the total molar amount of units derived from the diamine component contained in the polyamic acid. Furthermore, the content of aliphatic diamine-derived units is more preferably 75 to 90 mol%, and even more preferably 80 to 90 mol%, based on the total molar amount of units derived from the diamine component. The content of aromatic diamine-derived units in which two amine structures are located at meta positions on one aromatic ring of 65 to 80 mol%, and even more preferably 65 to 75 mol%, based on the total molar amount of units derived from the diamine component.

[0037] The polyamic acid used in the present invention can be obtained by reacting the above-mentioned tetracarboxylic acid component and diamine component in approximately equimolar amounts in a solvent, optionally with heating, until the desired viscosity (or molecular weight) is achieved. In the present invention, "approximately equimolar" means that the molar ratio of the tetracarboxylic acid component to the diamine component is about 0.90 to 1.10, preferably about 0.95 to 1.05.

[0038] The solvent used in the synthesis of polyamic acid is not particularly limited, and any known solvent used in the synthesis of polyamic acid can be selected and used. For example, from the viewpoint of the solubility of the tetracarboxylic acid component, the diamine component, and the polyamic acid, it is preferable to include at least one nitrogen-containing solvent. Examples of such solvents include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 1,1,3,3-tetramethylurea, 1,3-dimethyl-2-imidazolidinone, N,N-dimethylisobutyramide, N,N-dimethylpropionamide, and 3-methoxy-N,N-dimethylpropanamide.

[0039] Alternatively, it is also preferable to synthesize the polyamic acid in an aqueous solvent in the presence of a proton-accepting nitrogen-containing compound, which will be described later. Suitable aqueous solvents include those mentioned above.

[0040] The polyamic acid can be produced by adding a tetracarboxylic acid component, a diamine component, and a solvent to a reaction vessel equipped with a stirrer and stirring the mixture. The order of addition of these raw materials is not particularly limited. For example, a predetermined amount of the diamine component may be dissolved in the solvent and then the tetracarboxylic acid component may be added, or the tetracarboxylic acid component may be dissolved in the solvent and then the diamine component may be added, or the tetracarboxylic acid component and the diamine component may be added alternately to the solvent. If necessary, additives such as known reaction catalysts may be added at any time.

[0041] The reaction temperature is not particularly limited, but is preferably 0° C. or higher and 100° C. or lower, more preferably 10° C. or higher, and even more preferably 20° C. or higher. The reaction temperature is more preferably 90° C. or lower, and even more preferably 70° C. or lower. The polyamic acid may be partially imidized.

[0042] The content of polyamic acid in the polyamic acid / CNT aqueous dispersion of the present invention is 2% by mass or more, preferably 2.05 to 10% by mass, more preferably 2.1 to 7% by mass, even more preferably 2.15 to 5% by mass, and even more preferably 2.15 to 4.5% by mass. The content of polyamic acid is preferably 2 times or more, more preferably 2.25 times or more, and even more preferably 2.5 times or more, by mass relative to the mass of carbon nanotubes. While there is no particular upper limit, it is preferably 15 times or less. If the mass proportion of polyamic acid is too low, the dispersion stability of the carbon nanotubes will be insufficient.

[0043] Furthermore, the polyamic acid / CNT aqueous dispersion of the present invention preferably further contains a proton-accepting nitrogen-containing compound. By further containing a proton-accepting nitrogen-containing compound, the affinity of the polyamic acid for the aqueous solvent can be further increased, thereby further enhancing the dispersing effect of the polyamic acid on the carbon nanotubes in the polyamic acid / CNT aqueous dispersion.

[0044] The proton-accepting nitrogen-containing compound may be any compound having a proton-accepting nitrogen atom, but from the viewpoint of improving the solubility of the polyamic acid in aqueous solvents, a nitrogen-containing heterocyclic compound is preferred. Examples of the nitrogen-containing heterocyclic compounds include imidazole, 1-methylimidazole, 1-ethylimidazole, 1,2-dimethylimidazole (1,2-DMZ), 1,4-dimethylimidazole, 1,5-dimethylimidazole, 1,2,4-trimethylimidazole, 1-ethyl-2-methylimidazole, 1,4-dimethyl-2-ethylimidazole, 1-methoxyethylimidazole, 1-methyl-2-methoxyimidazole, 1-methyl-2-ethoxyimidazole, 1-methyl-4-methoxyimidazole, 1-ethoxymethyl-2-methylimidazole, 1-methyl-4-nitroimidazole, 1,2-dimethyl-5-nitroimidazole, 1,2-dimethyl-5-aminoimidazole, 1-methyl- Five-membered nitrogen-containing heterocyclic compounds such as 4-(2-aminoethyl)imidazole, 2-phenylimidazole, 1-methylimidazoline, 1,2-dimethylimidazoline, 1,2,4-trimethylimidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-heptylimidazoline, 1-methyl-2-undecylimidazoline, 1-methyl-2-heptadecylimidazoline, 1-methyl-2-ethoxymethylimidazoline, 1-ethoxymethyl-2-methylimidazoline, pyrrole, methylpyrrole, thiazole, oxazole, pyrazole, and isoxazole; and six-membered nitrogen-containing heterocyclic compounds such as pyridine, pyrazine, pyrimidine, pyridazine, triazine, and 2,6-lutidine. These may be used alone or in combination of two or more.

[0045] As the proton-accepting nitrogen-containing compound, a compound having an imidazole ring is preferred, and 1,5-dimethylimidazole (1,2-DMZ) is more preferred.

[0046] The content ratio of the proton-accepting nitrogen-containing compound in the polyamic acid / CNT aqueous dispersion of the present invention is 0.3 to 1 times, more preferably 0.4 to 1 times, even more preferably 0.5 to 1 times, and still more preferably 0.5 to 0.8 times, by mass relative to the mass of the polyamic acid.

[0047] The polyamic acid / CNT aqueous dispersion of the present invention may contain components other than the aqueous solvent, polyamic acid, carbon nanotubes, and the proton-accepting nitrogen-containing compound used as needed. Examples of such components include carbon black (e.g., furnace black, acetylene black, channel black, thermal black), fullerene, graphene, pH adjuster, negative electrode active material particles (e.g., Si, SiO), and positive electrode active material (e.g., LCO, LFP). The polyamic acid / CNT aqueous dispersion of the present invention allows carbon nanotubes to be highly dispersed without the use of known dispersants such as carboxymethyl cellulose, and therefore preferably does not contain any dispersants such as carboxymethyl cellulose. In particular, since carboxymethyl cellulose has insufficient heat resistance, it is preferable that the dispersion is substantially free of carboxymethyl cellulose (e.g., preferably less than 1 ppm by mass).

[0048] The method for preparing the polyamic acid / CNT aqueous dispersion of the present invention is not particularly limited, and can be prepared by mixing an aqueous solvent, polyamic acid, carbon nanotubes, and optionally a proton-accepting nitrogen-containing compound and other components. The method for mixing these is also not particularly limited, but from the perspective of further improving the dispersibility of carbon nanotubes, a preferred method is to disperse or dissolve the polyamic acid and optionally a proton-accepting nitrogen-containing compound in an aqueous solvent to prepare a polyamic acid-containing solution, and then disperse the carbon nanotubes in the polyamic acid-containing solution. In this case, if an aqueous solvent or a proton-accepting nitrogen-containing compound was used in synthesizing the polyamic acid, the polyamic acid-containing solution obtained by synthesis can be used as is, and the solids concentration can be adjusted as necessary before dispersing the carbon nanotubes.

[0049] The method for dispersing or dissolving the polyamic acid and the proton-accepting nitrogen-containing compound used as needed in the aqueous solvent is not particularly limited, and examples thereof include a method of adding the polyamic acid and the proton-accepting nitrogen-containing compound used as needed to the aqueous solvent and stirring and mixing them using a stirring device or a mixing device. In this case, when the polyamic acid and the proton-accepting nitrogen-containing compound used as needed are added to the aqueous solvent, they may be added all at once, or they may be added continuously or in portions.

[0050] Furthermore, the method for dispersing carbon nanotubes in a polyamic acid-containing solution is not particularly limited, but examples include a method in which carbon nanotubes are added to a polyamic acid-containing solution and then subjected to ultrasonic treatment or a stirring / dispersion treatment. For ultrasonic treatment, a bath-type or probe-type sonicator can be used. For stirring / dispersion treatment, a high-speed stirring device such as a homomixer or homogenizer, a media-type wet dispersion device such as an attritor, a bead mill, a sand mill, or a planetary mill, or a high-pressure dispersion treatment device such as a wet jet mill can be used. The treatment time for ultrasonic treatment or stirring / dispersion treatment is not particularly limited, but is preferably 10 minutes to 50 hours, more preferably 20 minutes to 10 hours, and even more preferably 30 minutes to 3 hours.

[0051] The polyamic acid / CNT aqueous dispersion of the present invention has a viscosity ratio V after 45 days of storage to that at the start of storage, calculated by the following formula (1) when stored at 25°C for 45 days. Ｒ＿４５ is in the range of 1.2 or less, and the viscosity change V after 45 days of storage relative to the start of storage, calculated by the following formula (2), Ｃ＿４５ The viscosity ratio V is in the range of 200 cps or less. Ｒ＿４５ = (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C after storage for 45 days) ４５ ) / (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) (1) Viscosity change amount V Ｃ＿４５ = | (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C after storage for 45 days) ４５ ) / -(Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) | (2)

[0052] According to the present invention, the viscosity ratio V after 45 days of storage to the viscosity at the start of storage is Ｒ＿４５ and the viscosity change amount V Ｃ＿４５By controlling the content of carbon nanotubes within the above range, the polyamic acid / CNT aqueous dispersion can be made to have excellent long-term storage stability (for example, stability when stored for 90 days or more, or when stored for 180 days or more), thereby achieving excellent quality retention. As a result, according to the present invention, when the polyamic acid / CNT aqueous dispersion is used, for example, in the production of an electrode for an electricity storage device, the excellent conductivity-imparting effect of the carbon nanotubes can be appropriately and stably imparted to the resulting electrode even after long-term storage (for example, after storage for 90 days or more, or after storage for 180 days or more), thereby enabling the resulting electrode to have low resistance, high capacity, and excellent capacity retention.

[0053] Viscosity ratio V after 45 days of storage to that at the start of storage Ｒ＿４５ is 1.2 or less, preferably 1.15 or less, more preferably 1.1 or less, and the viscosity ratio V after 45 days of storage to that at the start of storage is Ｒ＿４５ The lower limit of V is not particularly limited, but is preferably 0.9 or more. Ｒ＿４５ If the temperature is too high, the viscosity increases significantly after long-term storage, resulting in poor long-term storage stability.

[0054] In addition, the change in viscosity V after 45 days of storage compared to the start of storage Ｃ＿４５ is 200 cps or less, preferably 150 cps or less, more preferably 100 cps or less, and the viscosity ratio V after 45 days of storage to that at the start of storage Ｒ＿４５ The lower limit of the viscosity is not particularly limited, but is preferably 0 cps or more. Ｃ＿４５ If V is too large, the viscosity will increase significantly after long-term storage, resulting in poor long-term storage stability. Ｃ＿４５ As is clear from the above formula (2), the viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C after 45 days of storage is ４５ and the viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C at the start of storage. Ｉｎｉis the absolute value of the difference between

[0055] Viscosity ratio V after 45 days of storage to that at the start of storage Ｒ＿４５ and the viscosity change amount V Ｃ＿４５ The viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C at the start of storage can be calculated as follows: Ｉｎｉ and the viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C after 45 days of storage. ４５ is measured using a B-type viscometer or an E-type viscometer at a temperature of 25°C using an appropriate spindle depending on the viscosity at the start of storage, and the viscosity can be calculated from the measurement results obtained according to the above formulas (1) and (2). The shear rate in viscosity measurement is not particularly limited, but is preferably 3 to 30 s －１ The conditions are preferably in the range of 5 to 20 seconds. －１ The shear rate (rotational speed) is typically 16.5 to 19 s －１ range, or 5.5 to 9 seconds －１ The range is.

[0056] In addition, the viscosity V at the start of storage Ｉｎｉ When measuring the viscosity of the polyamic acid / CNT aqueous dispersion immediately after preparation, the viscosity is measured, and this is referred to as the viscosity V at the start of storage. Ｉｎｉ and the viscosity V Ｉｎｉ After measuring, the viscosity V after storing at 25°C for 45 days ４５ The viscosity at the start of storage V Ｉｎｉ The viscosity V is measured immediately after the aqueous dispersion is prepared, preferably within 24 hours after preparation, more preferably within 12 hours after preparation, and even more preferably within 6 hours after preparation. Ｉｎｉ When measuring the viscosity V at the start of storage, the polyamic acid / CNT aqueous dispersion is stirred again once by the above-mentioned ultrasonic treatment method or stirring / dispersion treatment method until the viscosity does not change substantially due to stirring, and then the viscosity of the polyamic acid / CNT aqueous dispersion after stirring is measured. ＩｎｉIn this case, the viscosity V Ｉｎｉ After measuring, the viscosity V after storing at 25°C for 45 days ４５ can be measured.

[0057] In the present invention, the viscosity V after storage for 45 days ４５ When measuring the viscosity, the storage temperature was set at 40°C and the viscosity was measured using a sample stored for 10 days. The measurement results were used as the viscosity V after 45 days of storage. ４５ The polyamic acid / CNT aqueous dispersion of the present invention may have a viscosity ratio V Ｒ＿４５ and the viscosity change amount V Ｃ＿４５ The above range also applies to the above.

[0058] The polyamic acid / CNT aqueous dispersion of the present invention is stored at 25° C. for 180 days, and the viscosity ratio V after 180 days of storage to that at the start of storage is calculated by the following formula (5): Ｒ＿１８０ , and the change in viscosity V after 180 days of storage relative to the start of storage, calculated by the following formula (6) Ｃ＿１８０ is not particularly limited, but is the viscosity ratio V after 180 days of storage to the viscosity at the start of storage. Ｒ＿１８０ is preferably kept low at 1.5 or less, more preferably 1.2 or less, and the change in viscosity V after 180 days of storage relative to the start of storage is Ｃ＿１８０ The viscosity ratio V is preferably kept low, at 400 cps or less, and more preferably at 200 cps or less. Ｒ＿１８０ = (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C after storage for 180 days) １８０ ) / (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) (5) Viscosity change amount V Ｃ＿１８０ = | (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C after storage for 180 days １８０ ) - (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) | (6)

[0059] The viscosity ratio V after 180 days of storage to that at the start of storage Ｒ＿１８０ and the viscosity change amount V Ｃ＿１８０ The viscosity ratio V after 45 days of storage to the start of storage is 180 days. Ｒ＿４５ and the viscosity change amount V Ｃ＿４５ It can be measured in the same manner as

[0060] <Polyamic Acid / Carbon Nanotube-Containing Aqueous Dispersion According to Another Aspect> The polyamic acid / carbon nanotube-containing aqueous dispersion (polyamic acid / CNT aqueous dispersion) of the present invention comprises an aqueous solvent, a polyamic acid, and carbon nanotubes, wherein the polyamic acid contains units derived from a tetracarboxylic acid component and units derived from a diamine component, and the polyamic acid may contain, as the units derived from the diamine component, units derived from an aliphatic diamine and / or units derived from an aromatic diamine in which two amine structures are located at meta positions of one aromatic ring, in a proportion of 50 mol % or more based on the total molar amount of the units derived from the diamine component.

[0061] In a polyamic acid / CNT aqueous dispersion according to another aspect of the present invention, the polyamic acid contains, as diamine component-derived units, units derived from an aliphatic diamine and / or units derived from an aromatic diamine in which two amine structures are located at the meta position of one aromatic ring, in a proportion of 50 mol % or more, based on the total molar amount of the diamine component-derived units, thereby making the polyamic acid / CNT aqueous dispersion excellent in long-term storage stability (e.g., stability after storage for 90 days or more or 180 days or more), thereby achieving excellent quality retention. As a result, when the polyamic acid / CNT aqueous dispersion is used, for example, in the production of an electrode for an electricity storage device, the excellent conductivity-imparting effect of the carbon nanotubes can be appropriately and stably imparted to the resulting electrode even after long-term storage (e.g., after storage for 90 days or more or 180 days or more), thereby making the resulting electrode low-resistance, high-capacity, and excellent capacity retention.

[0062] In the polyamic acid / CNT aqueous dispersion according to another aspect of the present invention, the tetracarboxylic acid component and diamine component constituting the polyamic acid can be the same as those described above, and the aqueous solvent and carbon nanotubes can also be the same as those described above. The polyamic acid / CNT aqueous dispersion according to another aspect of the present invention may also contain the proton-accepting nitrogen-containing compound and other components. In the polyamic acid / CNT aqueous dispersion according to another aspect of the present invention, the content of the polyamic acid in the aqueous dispersion is preferably 2% by mass or more, more preferably 2.05 to 10% by mass, even more preferably 2.1 to 7% by mass, and even more preferably 2.15 to 5% by mass.

[0063] <Binder Composition for Electrical Storage Device, Slurry for Electrode> The polyamic acid / CNT aqueous dispersion of the present invention (including polyamic acid / CNT aqueous dispersions according to other aspects of the present invention; the same applies hereinafter) can be used as a binder composition for an electrical storage device. Furthermore, an electrode slurry of the present invention contains the polyamic acid / CNT aqueous dispersion of the present invention as a binder composition for an electrical storage device and an active material. In this case, the polyamic acid acts as a binder for binding the active material, and, as described below, may be allowed to undergo an imidization reaction to form a polyimide, thereby acting as a binder, if necessary.

[0064] The active material may be either a negative electrode active material or a positive electrode active material, that is, the electrode slurry of the present invention may be a slurry for a negative electrode or a slurry for a positive electrode.

[0065] When the electrode slurry of the present invention is a slurry for a negative electrode, examples of the negative electrode active material, particularly as a negative electrode active material for a lithium secondary battery, include lithium metal, lithium alloys, carbon materials capable of absorbing and releasing lithium (e.g., easily graphitizable carbon, non-graphitizable carbon having a (002) plane spacing of 0.37 nm or more, and graphite having a (002) plane spacing of 0.34 nm or less), tin (simple substance), tin compounds, silicon (simple substance), silicon compounds, Li ４ Ti ５ O １２ Examples of suitable negative electrode active materials include lithium titanate compounds such as silicon (single element) and silicon compounds. These can be used alone or in combination of two or more. Because the use of the polyamic acid / CNT aqueous dispersion of the present invention significantly improves performance, silicon-containing negative electrode active materials, such as silicon (single element) or silicon compounds, are preferred. While silicon-containing negative electrode active materials, such as silicon (single element) or silicon compounds, have significantly higher theoretical capacities than graphite, they suffer from the problem of a relatively large volume expansion rate of the negative electrode active material itself during charging. However, the polyamic acid / CNT aqueous dispersion of the present invention, in which carbon nanotubes are appropriately dispersed, can appropriately mitigate such volume expansion, thereby more appropriately improving charge / discharge cycle performance.

[0066] The silicon-containing negative electrode active material is not particularly limited, but examples thereof include silicon (element), silicon compounds, partial substitution products of silicon, partial substitution products of silicon compounds, solid solutions of silicon compounds, etc. Specific examples of silicon compounds include SiO ｘ Silicon oxide represented by (0.05<x<1.95), SiC ｙ Silicon carbide represented by (0<y<1), SiN ｚ (0<z<4 / 3), and silicon alloys which are alloys of silicon and a different element M. In silicon alloys, the different element M is preferably at least one element selected from the group consisting of Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti.

[0067] Furthermore, the silicon partial substitution product is a compound in which a portion of the silicon contained in silicon (simple substance) and a silicon compound is substituted with a different element M. Specific examples of the different element M include B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn. Among these silicon-containing negative electrode active materials, silicon (simple substance), silicon oxide, or silicon alloy is preferred, and silicon (simple substance) or silicon oxide is more preferred.

[0068] Furthermore, when the electrode slurry of the present invention is a slurry for a negative electrode, it may contain, in addition to the negative electrode active material, a conductive material other than carbon nanotubes. The conductive material is not particularly limited as long as it is an electron-conductive material that does not undergo chemical change, and examples thereof include metal powders such as copper, nickel, titanium, and aluminum, and carbon materials other than carbon nanotubes.

[0069] When the electrode slurry of the present invention is a slurry for a positive electrode, the positive electrode active material is, in particular, a composite metal oxide containing lithium and at least one selected from cobalt, manganese, and nickel, which is used as a positive electrode active material for a lithium secondary battery. Examples of such lithium composite metal oxides include LiCoO ２ , LiMn ２ O ４ , LiNiO ２ , LiCo １－ｘ Ni ｘ O ２ (0.01<x<1), LiCo １／３ Ni １／３ Mn １／３ O ２ , LiNi １／２ Mn ３／２ O ４ , LiCo ０．９８ Mg ０．０２ O ２ In addition, LiCoO ２ and LiMn ２ O ４ , LiCoO ２ and LiNiO ２ , LiMn ２ O ４ and LiNiO２ They may be used in combination as follows.

[0070] When the electrode slurry of the present invention is a slurry for a positive electrode, it may contain, in addition to the positive electrode active material, a conductive material other than carbon nanotubes. The conductive material is not particularly limited as long as it is an electron-conductive material that does not undergo chemical change, and examples thereof include carbon materials other than carbon nanotubes.

[0071] The electrode slurry of the present invention can be produced by mixing the polyamic acid / CNT aqueous dispersion of the present invention described above, a negative electrode active material or a positive electrode active material, and an optional conductive material other than carbon nanotubes. In this case, an aqueous solvent may be further mixed, if necessary, to adjust the solid content concentration.

[0072] <Electrode for Electricity Storage Device> The electrode for an electricity storage device of the present invention is formed using the above-described electrode slurry of the present invention.

[0073] The electrode for an electricity storage device of the present invention can be produced, for example, by forming the above-described electrode slurry of the present invention into a sheet or the like.

[0074] The electrode for an electricity storage device of the present invention can be formed into a sheet by, for example, casting or applying the above-described electrode slurry of the present invention onto a conductive current collector such as aluminum foil or copper foil, heating the slurry to remove the aqueous solvent, and optionally applying pressure to form an active material layer on the current collector. In this case, the heating during the formation of the active material layer on the current collector may promote an imidization reaction of the polyamic acid contained in the electrode slurry, converting the polyamic acid as a polyimide precursor into a polyimide.

[0075] In this case, the polyimide preferably contains, as the main component (50 mol % or more), more preferably 75 mol % or more, and even more preferably 90 mol % or more, a polyimide containing a repeating unit represented by the following formula (4): That is, the polyimide may be a partially imidized polyimide in which a portion of the amic acid structures contained in the polyamic acid as the polyimide precursor are imidized, or a fully imidized polyimide in which all of the amic acid structures contained in the polyamic acid as the polyimide precursor are imidized, or a mixture of these. In the above formula (4), X １ represents one or more tetravalent groups obtained by removing a carboxyl group from a tetracarboxylic acid component, and Y １ represents one or more divalent groups obtained by removing an amino group from a diamine component.

[0076] The method for imidizing the polyamic acid as a polyimide precursor is not particularly limited, but examples include chemical imidization and / or thermal imidization by heat treatment of the polyamic acid. Taking thermal imidization as an example, the maximum heating temperature in the heat treatment is typically 150°C or higher, preferably 200°C or higher, more preferably 250°C or higher, and even more preferably 350°C or higher. The upper limit of the heat treatment temperature is any temperature that does not deteriorate the properties, and is preferably 450°C or lower, more preferably 430°C or lower, and even more preferably 400°C or lower. While the heat treatment can be carried out in an air atmosphere, it is preferably carried out in an inert gas atmosphere, more preferably a nitrogen gas atmosphere. Chemical imidization can be carried out under milder heat treatment conditions than thermal imidization, depending on the type of additive, such as a chemical imidization catalyst. For example, the heat treatment may be carried out at a temperature range of usually 100°C or higher, preferably 120°C or higher, more preferably 150°C or higher, and even more preferably 200°C or higher, and usually 360°C or lower, preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 220°C or lower.

[0077] The heat treatment for chemical imidization and / or thermal imidization may be carried out in stages. For example, a first heat treatment is preferably carried out at a relatively low temperature of 100°C or higher and 170°C or lower for 0.5 minutes to 30 minutes, followed by a second heat treatment at a temperature above 170°C and 220°C or lower for 0.5 minutes to 30 minutes, followed by a third heat treatment at a high temperature above 220°C and lower than 350°C for 0.5 minutes to 30 minutes, and then a fourth high-temperature heat treatment from 350°C or higher to the maximum heating temperature. The heat treatment is preferably carried out continuously. For example, the heat treatment is preferably carried out from a relatively low temperature of 100°C or higher and 170°C or lower to the maximum heating temperature. The temperature rise rate is not particularly limited, but is preferably 1°C / min to 30°C / min, and particularly preferably 2°C / min to 20°C / min. The above range is preferable because it can suppress foaming due to a sudden rise in temperature.

[0078] The thickness of the active material layer in the electrode for an electricity storage device of the present invention may be appropriately determined depending on the application and the desired capacity. It is not limited, but is preferably in the range of 0.1 μm or more and 500 μm or less. It is more preferably 1 μm or more, even more preferably 10 μm or more, even more preferably 20 μm or more, and more preferably 300 μm or less, even more preferably 100 μm or less, and even more preferably 50 μm or less.

[0079] <Electricity storage device> The electricity storage device of the present invention includes the electrode for the electricity storage device of the present invention described above. The electricity storage device includes electricity storage devices such as lithium batteries, electric double layer capacitors, and lithium ion capacitors. Among these, lithium batteries using a lithium salt as the electrolyte salt are preferred, and lithium secondary batteries are suitable.

[0080] The lithium secondary battery includes a positive electrode, a negative electrode, a non-aqueous electrolyte, a separator, and other components, and can employ any known configuration required for a lithium secondary battery. In the present invention, the above-described electrode for the power storage device of the present invention is used as the positive electrode and / or the negative electrode. The lithium secondary battery may be a lithium polymer battery using a gel electrolyte as the electrolyte, or an all-solid-state battery using an inorganic solid electrolyte such as an oxide or sulfide.

[0081] The non-aqueous electrolyte is a non-aqueous solvent in which an electrolyte salt is dissolved. There are no particular limitations on the non-aqueous electrolyte, and various types can be used.

[0082] The electrolyte salt used is one that dissolves in a non-aqueous electrolyte, such as LiPF ６ , LiBF ４ , LiPO ２ F ２ , LiN(SO ２ F) ２ , LiClO ４ Inorganic lithium salts such as LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiCF ３ SO ３ , LiC(SO ２ CF ３ ) ３ , LiPF ４ (CF ３ ) ２ , LiPF ３ (C ２ F ５ ) ３ , LiPF ３ (CF ３ ) ３ , LiPF ３ (iso-C ３ F ７ ) ３ , LiPF ５ (iso-C ３ F ７ ) and lithium salts containing chain-like fluorinated alkyl groups such as (CF ２ )２ (SO ２ ) ２ NLi, (CF ２ ) ３ (SO ２ ) ２ Examples include lithium salts containing a cyclic fluorinated alkylene chain such as NLi, and lithium salts having an oxalate complex as the anion such as lithium bis[oxalate-O,O']borate and lithium difluoro[oxalate-O,O']borate.

[0083] The concentration of all of these electrolyte salts dissolved in the non-aqueous solvent is preferably 0.3 M or more, more preferably 0.5 M or more, and even more preferably 0.7 M or more. The upper limit is preferably 2.5 M or less, more preferably 2.0 M or less, and even more preferably 1.5 M or less.

[0084] Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, chain esters, ethers, amides, phosphate esters, sulfones, lactones, nitriles, and S═O bond-containing compounds, and the non-aqueous solvent preferably contains a cyclic carbonate. Note that the term "chain ester" is used as a concept that includes chain carbonates and chain carboxylic acid esters.

[0085] Examples of cyclic carbonates include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one (FEC), trans- or cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter collectively referred to as "DFEC"), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and 4-ethynyl-1,3-dioxolan-2-one (EEC). The proportion of cyclic carbonates having alkylene chains in all cyclic carbonates is preferably 55% to 100% by volume, more preferably 60% by volume or more, and even more preferably 90% by volume or less.

[0086] In addition, non-aqueous solvents are preferably used in combination to achieve appropriate physical properties. Examples of such combinations include a combination of a cyclic carbonate and a chain ester. Suitable examples of the chain ester include one or more asymmetric chain carbonates selected from methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate; one or more symmetric chain carbonates selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate; pivalic acid esters such as methyl pivalate, ethyl pivalate, and propyl pivalate; and one or more chain carboxylic acid esters selected from methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate (EA).

[0087] <Electromagnetic Wave Shielding Composition> The polyamic acid / CNT aqueous dispersion of the present invention can be used as an electromagnetic wave shielding composition for forming an electromagnetic wave shielding paint, an electromagnetic wave shielding film, or the like.

[0088] The electromagnetic wave shielding composition of the present invention may contain, as optional components, a leveling agent, a dispersing agent, a crosslinking agent, a catalyst, a water-soluble antioxidant, an antifoaming agent, a rheology control agent, a neutralizing agent, a thickener, an inorganic filler, etc.

[0089] Examples of the leveling agent include a silicone-based leveling agent, a fluorine-based leveling agent, a polyether-based leveling agent, a polyester-based leveling agent, and an acrylic-based leveling agent.

[0090] Examples of dispersants include cationic dispersants, anionic dispersants, amphoteric dispersants, nonionic dispersants, and polymeric dispersants.

[0091] Examples of inorganic fillers include silica such as colloidal silica, hollow silica, and fumed silica; metal oxides such as titania and zirconia; and organic-inorganic composites such as a core-shell type acrylic-silica composite in which a thermoplastic or thermosetting acrylic resin is coated with silica, a core-shell type melamine-silica composite in which a melamine resin is coated with silica, a core-shell type acrylic-silica composite in which silica is coated with a thermoplastic or thermosetting acrylic resin, a core-shell type melamine-silica composite in which silica is coated with a melamine resin, and an acrylic-silica composite in which small silica particles are supported by a thermoplastic or thermosetting acrylic resin.

[0092] When the electromagnetic wave shielding composition of the present invention contains the above-mentioned optional components in addition to the above-mentioned polyamic acid / CNT aqueous dispersion of the present invention, it can be produced by mixing the above-mentioned polyamic acid / CNT aqueous dispersion of the present invention with the above-mentioned optional components. At this time, an aqueous solvent may be further mixed, if necessary, to adjust the solids concentration.

[0093] <Electromagnetic Wave Shielding Coating Film> The electromagnetic wave shielding coating film of the present invention is a coating film formed using the electromagnetic wave shielding composition of the present invention.

[0094] The electromagnetic wave shielding coating film of the present invention can be formed, for example, by casting or applying the electromagnetic wave shielding composition of the present invention onto at least one surface of a substrate, followed by heat treatment to remove the aqueous solvent. In this case, as in the case of the electrode for the electricity storage device described above, the imidization reaction of the polyamic acid contained in the electromagnetic wave shielding composition may be promoted by heating, and the polyamic acid as a polyimide precursor may be converted into a polyimide.

[0095] The electromagnetic wave shielding coating film may be formed by directly casting or applying the electromagnetic wave shielding composition onto a substrate, or may be formed by forming another layer such as a primer layer on the substrate in advance, and then casting or applying the composition onto the formed layer.

[0096] <Electromagnetic wave shielding laminate> The electromagnetic wave shielding laminate of the present invention comprises the electromagnetic wave shielding coating film of the present invention and a substrate. The electromagnetic wave shielding laminate may further comprise a dielectric layer, an adhesive layer, a protective layer, a decorative layer, etc.

[0097] The dielectric layer is preferably present on the surface of the electromagnetic wave shielding coating film opposite to the surface that contacts the substrate. The dielectric layer is not particularly limited in composition as long as it can generate dielectric loss and absorb electromagnetic waves, but is preferably formed from a composition containing: a synthetic resin such as polyurethane, acrylic resin, ethylene-vinyl acetate copolymer, or polyvinyl chloride; a rubber material such as polyisoprene rubber, polystyrene-butadiene rubber, polybutadiene rubber, chloroprene rubber, or acrylonitrile-butadiene rubber; a carbon material such as carbon nanotubes, graphene, fullerene, or carbon nanofibers; titanium oxide, polyvinylidene fluoride, polyester resin, glass, or silicone rubber.

[0098] The adhesive layer is a layer containing an adhesive composition, and is preferably formed on the surface of the substrate opposite to the surface on which the electromagnetic wave shielding coating film is present.

[0099] The protective layer is a layer that prevents the electromagnetic wave shielding properties from being reduced due to mechanical impact or humidity in the air, and examples of materials for the protective layer include polyethylene terephthalate (PET) and polyethylene (PE).

[0100] The decorative layer is a layer formed to improve the appearance of the electromagnetic wave shielding laminate and to conceal the internal structure, such as electronic circuits, and examples of materials for the decorative layer include resins such as polyethylene terephthalate (PET) and polyethylene (PE), and metals such as aluminum, gold, platinum, copper, silver, and zinc.

[0101] The electromagnetic wave shielding laminate of the present invention can be used as an electromagnetic wave shield, for example, in semiconductor packages, conductive gaskets, shielding films, shielding cases, communication devices, sensors, clothing, and the interior and exterior decoration of buildings.

[0102] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these.

[0103] The abbreviations for the compounds used in the following examples are as follows: s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride ODPA: 4,4'-oxydiphthalic dianhydride DMD: 1,10-diaminodecane 3,5-DABA: 3,5-diaminobenzoic acid MPD: m-phenylenediamine PPD: p-phenylenediamine ODA: 4,4'-diaminodiphenyl ether 1,2-DMZ: 1,2-dimethylimidazole

[0104] Example 1: 348.1408 g of ion-exchanged water, 63.4759 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 31.6003 g of 1,10-diaminodecane (DMD), 4.9238 g of 3,5-diaminobenzoic acid (3,5-DABA), and 51.8592 g of 1,2-dimethylimidazole (1,2-DMZ) were placed in a stirring vessel equipped with a stirrer and a nitrogen inlet tube, and the mixture was stirred under a nitrogen atmosphere at 70°C for 5 hours to react, yielding an aqueous solution of polyamic acid. The molar ratio of s-BPDA:DMD:3,5-DABA was 100:85:15.

[0105] Next, the resulting aqueous solution of polyamic acid was diluted with ion-exchanged water, after which 0.4 g of single-walled carbon nanotubes (SWCMT: manufactured by OCSiAL, product name "TUBALL (registered trademark) 01RW03", hereinafter simply referred to as SWCNT) was added, and dispersion treatment using a homogenizer was carried out for several passes to obtain 100 g of a polyamic acid / CNT aqueous dispersion. The resulting polyamic acid / CNT aqueous dispersion had a polyamic acid content of 2.17 mass %, a 1,2-dimethylimidazole (1,2-DMZ) content of 1.1235 mass %, and a single-walled carbon nanotube (SWCMT) content of 0.4 mass %.

[0106] [Viscosity at the start of storage V Ｉｎｉ , the viscosity ratio V after 45 days of storage to the viscosity at the start of storage Ｒ＿４５, viscosity change amount V Ｃ＿４５ The obtained polyamic acid / CNT aqueous dispersion was then divided into two portions, and one portion was used to measure the viscosity using a Brookfield viscometer at 25°C with a No. SC4-21 rotor at a rotation speed such that the shear rate was as shown in Table 1. The viscosity V at the start of storage was Ｉｎｉ The results are shown in Table 1. The other polyamic acid / CNT aqueous dispersion was stored at a temperature of 25°C for 45 days, and the viscosity of the polyamic acid / CNT aqueous dispersion stored for 45 days was measured under the same conditions as above. ４５ The viscosity V at the start of storage was then calculated. Ｉｎｉ and viscosity V after 45 days of storage ４５ From the above, according to the above formula (1) and formula (2), the viscosity ratio V Ｒ＿４５ and the viscosity change amount V Ｃ＿４５ The results are shown in Table 1.

[0107] [Viscosity ratio V after 180 days of storage to that at the start of storage Ｒ＿１８０ , viscosity change amount V Ｃ＿１８０ The obtained polyamic acid / CNT aqueous dispersion was stored at a temperature of 25° C. for 180 days, and the viscosity of the polyamic acid / CNT aqueous dispersion stored for 180 days was measured under the same conditions as above. １８０ The viscosity V at the start of storage was then calculated. Ｉｎｉ and viscosity V after storage for 180 days １８０ From the above, according to the above formulas (5) and (6), the viscosity ratio V after 180 days of storage to the viscosity at the start of storage is calculated. Ｒ＿１８０ and the viscosity change amount V Ｃ＿１８０ The results are shown in Table 1.

[0108] Examples 2 to 4 Polyamic acid / CNT aqueous dispersions were obtained and evaluated in the same manner as in Example 1, except that the content ratios of polyamic acid, 1,2-dimethylimidazole (1,2-DMZ), and single-walled carbon nanotubes (SWCMT) were changed to those shown in Table 1. The results are shown in Table 1.

[0109] [Viscosity ratio V after 90 days of storage to that at the start of storage Ｒ＿９０ , viscosity change amount V Ｃ＿９０ The polyamic acid / CNT aqueous dispersions obtained in Examples 3 and 4 were stored at a temperature of 25° C. for 90 days, and the viscosity of the polyamic acid / CNT aqueous dispersions stored for 90 days was measured under the same conditions as above. ９０ The viscosity at the start of storage, V Ｉｎｉ and viscosity V after storage for 90 days ９０ From the above, the viscosity ratio V after 90 days of storage to the viscosity at the start of storage is calculated according to the following formulas (7) and (8). Ｒ＿９０ and the viscosity change amount V Ｃ＿９０ The results are shown in Table 1. Viscosity ratio V Ｒ＿９０ = (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C after storage for 90 days) ９０ ) / (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) (7) Viscosity change amount V Ｃ＿９０ = | (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C after 90 days of storage) ９０ ) - (Viscosity V of the polyamic acid / CNT aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) | (8)

[0110] Example 5 A polyamic acid / CNT aqueous dispersion was obtained and evaluated in the same manner as in Example 1, except that when obtaining the polyamic acid, m-phenylenediamine (MPD) and p-phenylenediamine (PPD) were used as the diamine components in the proportions shown in Table 1, and the polyamic acid content, 1,2-dimethylimidazole (1,2-DMZ) content, and single-walled carbon nanotube (SWCMT) content were changed to those shown in Table 1. The results are shown in Table 1.

[0111] Comparative Examples 1 and 2 A polyamic acid / CNT aqueous dispersion was obtained and evaluated in the same manner as in Example 1, except that when obtaining the polyamic acid, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and 4,4'-oxydiphthalic dianhydride (ODPA) were used as the tetracarboxylic acid components in the proportions shown in Table 1, and p-phenylenediamine (PPD) and 4,4'-diaminodiphenyl ether (ODA) were used as the diamine components in the proportions shown in Table 1, and the polyamic acid content and the 1,2-dimethylimidazole (1,2-DMZ) content were changed to those shown in Table 1. The results are shown in Table 1.

[0112] Comparative Examples 3 and 4 A polyamic acid / CNT aqueous dispersion was obtained and evaluated in the same manner as in Example 1, except that when obtaining the polyamic acid, 4,4'-diaminodiphenyl ether (ODA) was used as the diamine component in the proportion shown in Table 1, and the polyamic acid content and the 1,2-dimethylimidazole (1,2-DMZ) content were changed to those shown in Table 1. The results are shown in Table 1.

[0113] Comparative Example 5 A polyamic acid / CNT aqueous dispersion was obtained and evaluated in the same manner as in Example 1, except that when obtaining the polyamic acid, p-phenylenediamine (PPD) was used as the diamine component in the proportion shown in Table 1, and the content proportions of polyamic acid and 1,2-dimethylimidazole (1,2-DMZ) were changed to those shown in Table 1. The results are shown in Table 1.

[0114] In the table, "-" indicates that the measurement was not performed.

[0115] As shown in Table 1, the viscosity ratio V after 45 days of storage to the initial value Ｒ＿４５ The viscosity change V after 45 days of storage relative to the start of storage is 1.2 or less. Ｃ＿４５ In the polyamic acid / CNT aqueous dispersions of Examples 1 to 5, the viscosity ratio V after 180 days of storage to that at the start of storage was 200 cps or less. Ｒ＿１８０, and the change in viscosity V after 180 days of storage relative to the start of storage Ｃ＿１８０ (or the viscosity ratio V Ｒ＿９０ , and the change in viscosity V after 90 days of storage relative to the start of storage Ｃ＿９０ Therefore, according to the polyamic acid / CNT aqueous dispersions of Examples 1 to 5, due to the good dispersibility of carbon nanotubes and the excellent long-term storage stability, when used in the production of electrodes for electricity storage devices, the excellent conductivity-imparting effect of the carbon nanotubes can be appropriately and stably imparted to the resulting electrode even after long-term storage (for example, even after storage for 180 days or more or 90 days or more), and it can be said that this enables the resulting electrode to have low resistance, high capacity, and excellent capacity retention characteristics.

[0116] Although not shown in Table 1, in Example 3, an E-type viscometer was used instead of a B-type viscometer, and the shear rate was 20 s －１ In this case, the viscosity ratio V Ｒ＿４５ , viscosity change amount V Ｃ＿４５ As a result of the measurement, the viscosity ratio V Ｒ＿４５ : 0.93, viscosity change amount V Ｃ＿４５ : 80 cps, and for Example 4, a shear rate of 6.8 s －１ In this case, the viscosity ratio V Ｒ＿４５ , viscosity change amount V Ｃ＿４５ As a result of the measurement, the viscosity ratio V Ｒ＿４５ : 0.99, viscosity change amount V Ｃ＿４５ In Example 4, the viscosity was measured using a Brookfield viscometer at a shear rate of 6.8 s －１ In this case, the viscosity ratio V Ｒ＿１８０ , and the viscosity change amount V Ｃ＿１８０ The viscosity ratio V Ｒ＿１８０ , and the viscosity change amount V Ｃ＿１８０ The value of is the shear rate of 17.0 s －１ Almost the same value was obtained.

[0117] On the other hand, the viscosity ratio V after 45 days of storage to that at the start of storage Ｒ＿４５ is greater than 1.2, or the change in viscosity V from the start of storage after 45 days of storage is Ｃ＿４５ The polyamic acid / CNT aqueous dispersions of Comparative Examples 1 to 6, in which the viscosity was more than 200 cps, had a viscosity ratio V Ｒ＿１８０ , and the change in viscosity V after 180 days of storage relative to the start of storage Ｃ＿１８０ (or the viscosity ratio V after 90 days of storage to the viscosity at the start of storage) Ｒ＿９０ , and the change in viscosity V after 90 days of storage relative to the start of storage Ｃ＿９０ The polyamic acid / CNT aqueous dispersion of Comparative Example 6 had a viscosity V Ｉｎｉ was too high, and the viscosity ratio V Ｒ＿４５ , viscosity change amount V Ｃ＿４５ , the viscosity ratio V after 180 days of storage to the viscosity at the start of storage Ｒ＿１８０ , viscosity change amount V Ｃ＿１８０ None of these could be measured.

[0118] In addition, for the polyamic acid / CNT aqueous dispersions of Examples 1 to 5, the viscosity ratio V Ｒ＿４５ and the viscosity change amount V Ｃ＿４５ The results were the same as those obtained when the product was stored at 25°C for 45 days.

[0119] The polyamic acid / CNT aqueous dispersion of the present invention is suitable for use, for example, in the production of electrodes for electricity storage devices. Furthermore, by forming an electromagnetic wave shielding composition containing the polyamic acid / CNT aqueous dispersion of the present invention into a coating film, it is possible to obtain, for example, an electromagnetic wave shielding coating film that is suitable as an electromagnetic wave shielding film having excellent heat resistance and durability.

Claims

1. A polyamic acid / carbon nanotube-containing aqueous dispersion comprising an aqueous solvent, polyamic acid, and carbon nanotubes, wherein the content of the polyamic acid in the aqueous dispersion is 2 mass% or more, and the aqueous dispersion is stored at 25°C for 45 days, and the viscosity ratio V after storage for 45 days relative to the viscosity at the start of storage is calculated by the following formula (1): Ｒ＿４５ The aqueous dispersion is stored at 25° C. for 45 days, and the viscosity change V after 45 days of storage relative to the start of storage is calculated by the following formula (2): Ｃ＿４５ A polyamic acid / carbon nanotube-containing aqueous dispersion having a viscosity ratio V of 200 cps or less. Ｒ＿４５ = (Viscosity V of the aqueous dispersion at 25°C after storage for 45 days) ４５ ) / (Viscosity V of the aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) (1) Viscosity change amount V Ｃ＿４５ = | (Viscosity V of the aqueous dispersion at 25 ° C. after storage for 45 days ４５ ) - (Viscosity V of the aqueous dispersion at 25°C at the start of storage Ｉｎｉ ) | (2) 2. A polyamic acid / carbon nanotube-containing aqueous dispersion comprising an aqueous solvent, a polyamic acid, and carbon nanotubes, wherein the polyamic acid contains units derived from a tetracarboxylic acid component and units derived from a diamine component, and the polyamic acid contains, as the units derived from the diamine component, units derived from an aliphatic diamine and / or units derived from an aromatic diamine in which two amine structures are located at the meta position of one aromatic ring, in a proportion of 50 mol % or more based on the total molar amount of the units derived from the diamine component.

3. The polyamic acid / carbon nanotube-containing aqueous dispersion according to claim 1 or 2, further comprising a proton-accepting nitrogen-containing compound.

4. The polyamic acid / carbon nanotube-containing aqueous dispersion according to claim 1 or 2, wherein the carbon nanotubes are single-walled carbon nanotubes.

5. The polyamic acid / carbon nanotube-containing aqueous dispersion according to claim 1 or 2, wherein the content of the carbon nanotubes in the aqueous dispersion is 0.4 mass % or more.

6. The polyamic acid / carbon nanotube-containing aqueous dispersion according to claim 1 or 2, wherein the aqueous solvent contains water.

7. A binder composition for an electrical storage device, comprising the polyamic acid / carbon nanotube-containing aqueous dispersion according to claim 1 or 2.

8. A slurry for an electrode comprising the binder composition for an electrical storage device according to claim 7 and an active material.

9. An electrode for an electricity storage device, which is made using the electrode slurry according to claim 8.

10. An electricity storage device comprising the electrode for an electricity storage device according to claim 9.

11. An electromagnetic wave shielding composition comprising the polyamic acid / carbon nanotube-containing aqueous dispersion according to claim 1 or 2.

12. An electromagnetic wave shielding coating film obtained by using the electromagnetic wave shielding composition according to claim 11.

13. An electromagnetic wave shielding laminate comprising the electromagnetic wave shielding coating film according to claim 12 and a substrate.

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