JP7823647B2 - Dispersion composition - Google Patents

Description

The present invention relates to a dispersion composition and a dispersant.

Nano-sized materials (i.e., nanoparticles) such as nanocarbons and metal nanoparticles possess excellent electrical, mechanical, and thermal stability properties, and their potential applications and practical use as nanomaterials in various fields are being explored. These nanoparticles are sometimes dispersed in a medium to utilize their functions, or nanoparticles dispersed in a liquid phase are applied to a substrate to create functional materials. In such cases, to fully utilize the nanoparticles' properties, it is desirable to uniformly disperse the particles in the dispersion medium. Therefore, the use of polyimides as polymeric dispersants has been proposed as one method for suppressing nanoparticle aggregation and improving particle dispersibility (see Non-Patent Document 1). Non-Patent Document 1 discloses the use of polyimides containing sulfonic acid group-containing diamine units as dispersants for carbon nanotubes (CNTs).

"General Overview of Carbon Nanotube Dispersion Technology," Journal of the Society of Rubber Science and Technology of Japan, 2016, Vol. 89, No. 1, pp. 15-21

Polyimides having anionic groups on the side chains, such as the polyimide dispersant described in Non-Patent Document 1, do not have sufficiently high solubility in organic solvents. Therefore, when an organic solvent is used as a dispersion medium for dispersing a substance to be dispersed, such as nanocarbon, the dispersant may not be sufficiently dissolved in the dispersion medium, and there is a concern that the dispersibility of the substance to be dispersed and the dispersion stability over time may be reduced.
Furthermore, when using a dispersion composition such as nanocarbon in devices that form electrodes on a film, it is necessary to remove the dispersant to expose the nanocarbon on the surface. However, when polyimide is used as the dispersant, the dispersant is not sufficiently removable, and there are concerns about the impact on the device due to the inability to remove the dispersant.

The present invention has been made in consideration of the above-mentioned problems, and its main object is to provide a dispersion composition and a dispersant that have excellent dispersibility and dispersion stability of the dispersed substance and excellent dispersant removal properties after film formation.

The inventors conducted extensive research to solve the above problems and discovered that the above problems can be solved by using a polyamic acid having a specific structure. That is, the present invention provides the following means:

<1> A dispersion composition containing a substance to be dispersed, a dispersion medium, and a polyamic acid having a specific structure which is at least one type selected from the group consisting of a steroid structure and a structure represented by the following formula (1):
*-L ¹ -R ¹ -R ² -R ³ -R ⁴ ...(1)
(In formula (1), L ¹ is a single bond, —O—, —CO—, —COO-* ¹ , —OCO-* ¹ , —NR ⁵ —, —NR ⁵ —CO-* ¹ , —CO-NR ⁵ —* ¹ , an alkanediyl group having 1 to 6 carbon atoms, —O-R ⁶ —* ¹ , or —R ⁶ —O-* ¹ (wherein R ⁵ is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms, and R ⁶ is an alkanediyl group having 1 to 3 carbon atoms. * ¹ is a bond to R ¹ ). R ¹ and R ³ are each independently a single bond, a substituted or unsubstituted phenylene group, or a substituted or unsubstituted cycloalkylene group. ^{R 2} is a single bond, a substituted or unsubstituted phenylene group, a substituted or unsubstituted cycloalkylene group, or —R ⁷ -B ¹ -R ⁸ - (wherein R ⁷ and R ⁸ are each independently a substituted or unsubstituted phenylene group or a substituted or unsubstituted cycloalkylene group, and B ¹ is a single bond, —O—, —COO-* ² , —OCO-* ² , —OCH ₂ -* ² , —CH ₂ O-* ² , or an alkanediyl group having 1 to 3 carbon atoms. * ² is a bond to R ⁸ ). R ⁴ is a hydrogen atom, a fluorine atom, a cyano group, * ³ -OCO-CH ₃ (where * ³ is R indicates a bond to ^{R 3.} ), an alkyl group having 1 to 18 carbon atoms, a fluoroalkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, a fluoroalkoxy group having 1 to 18 carbon atoms, or a monovalent group in which at least one hydrogen atom of an alkyl group having 1 to 18 carbon atoms has been substituted with a cyano group. However, when all of R ¹ , R ² and R ³ are single bonds, or the total number of benzene rings and cycloalkane rings possessed by R ¹ , R ² and R ³ is 1, R ⁴ is an alkyl group having 3 to 18 carbon atoms, a fluoroalkyl group having 3 to 18 carbon atoms, an alkoxy group having 3 to 18 carbon atoms, or a fluoroalkoxy group having 3 to 18 carbon atoms. * indicates a bond.)
<2> A dispersant containing the polyamic acid.

According to the present invention, a dispersion composition can be obtained that has excellent dispersibility and dispersion stability of the dispersed substance and excellent dispersant removal performance after film formation. Furthermore, a dispersant can be obtained that has excellent dispersibility and dispersion stability of the dispersed substance and excellent removal performance after film formation.

1 is an AFM image showing that the dispersant removability was good (A) in the evaluation of an example of the present invention. 1 is an AFM image showing that the dispersant removability was poor (C) in the evaluation of the comparative example of the present invention.

The dispersion composition of the present disclosure contains (A) a substance to be dispersed, (B) a dispersion medium, and (C) a polyamic acid. Each component contained in the dispersion composition of the present disclosure, as well as other components that may be optionally blended as needed, will be described below.
In this specification, the term "hydrocarbon group" includes chain hydrocarbon groups, alicyclic hydrocarbon groups, and aromatic hydrocarbon groups. "Chain hydrocarbon group" refers to a straight-chain hydrocarbon group or a branched hydrocarbon group that does not contain a cyclic structure in the main chain and is composed only of a chain structure. However, it may be saturated or unsaturated. "Alicyclic hydrocarbon group" refers to a hydrocarbon group that contains only an alicyclic hydrocarbon structure as a ring structure and does not contain an aromatic ring structure. However, it does not have to be composed only of an alicyclic hydrocarbon structure and may also contain a chain structure as part of it. "Aromatic hydrocarbon group" refers to a hydrocarbon group that contains an aromatic ring structure as a ring structure. However, it does not have to be composed only of an aromatic ring structure and may contain a chain structure or an alicyclic hydrocarbon structure as part of it.

<(A) Dispersed element>
The dispersed substance is a substance to be dispersed in a dispersion medium, i.e., a dispersoid. As the dispersed substance, at least one type selected from the group consisting of inorganic particles and organic particles can be used, with inorganic particles being preferred. The shape of the dispersed substance is not particularly limited, and examples include spherical, rod-like, fibrous, flat, and disc-like shapes. The primary particle diameter of the dispersed substance is preferably 10 μm or less, more preferably 1 μm or less, and even more preferably 200 nm or less. The primary particle diameter of the dispersed substance is preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 5 nm or more. The "primary particle diameter of the dispersed substance" referred to here is a value determined by measuring the d50 value using a laser diffraction/scattering method.

Inorganic particles contained in the dispersion composition of the present disclosure include, for example, carbon, metal particles, semi-metal particles, silica, inorganic salts, quantum dots, etc. Specific examples of these include carbon such as carbon black, carbon fiber, carbon nanotubes, graphite, fullerenes, carbon nanohorns, etc.; metal particles such as elemental metals, metal oxides, metal carbides, metal nitrides, etc.; semi-metal particles such as semi-metal oxides, semi-metal carbides, and semi-metal nitrides, etc.; silica such as wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), colloidal silica, precipitated silica, calcium silicate, aluminum silicate, and surface-modified silica, etc.; inorganic salts such as sulfates (calcium sulfate, barium sulfate, etc.), carbonates (calcium carbonate, magnesium carbonate, barium carbonate, etc.), and phosphates (calcium phosphate, etc.); and quantum dots such as perovskite quantum dots, carbon-based quantum dots, and lead sulfide quantum dots, etc.

Note that carbon fibers include carbon nanofibers. Carbon nanotubes include single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes. Furthermore, carbon nanotubes may consist solely of carbon, or may have part of their structure substituted with other elements or chemically modified, or may be composites with metals (e.g., gold, silver, copper, aluminum, nickel, cobalt, titanium, platinum, etc.).

In one embodiment of the dispersion composition of the present disclosure, at least one substance selected from the group consisting of metal particles and semi-metal particles (hereinafter also referred to as "metal particles, etc.") can be preferably used as the dispersed substance. In another embodiment, at least one substance selected from the group consisting of rod-shaped nanostructures and rod-shaped molecules (hereinafter also referred to as "rod-shaped nanostructures, etc.") can be preferably used as the dispersed substance. Examples of rod-shaped molecules include dichroic dyes, and examples of rod-shaped nanostructures include dye aggregates, quantum rods, metal nanorods, carbon nanotubes, proteins, nucleic acids, viruses, etc. When the dispersed substance is at least one substance selected from the group consisting of rod-shaped nanostructures and rod-shaped molecules, inorganic particles can be preferably used as the dispersed substance, with carbon nanotubes and metal nanorods being particularly preferred.

The dispersed substance is preferably nanocarbon. Nanocarbon refers to carbon with a primary particle diameter of 1 nm or more and less than 1000 nm. The lower limit of the primary particle diameter of nanocarbon is preferably 2 nm, more preferably 5 nm. On the other hand, the upper limit of the primary particle diameter of nanocarbon is preferably 500 nm, more preferably 200 nm. As the nanocarbon, at least one selected from the group consisting of carbon black, carbon fiber, carbon nanotubes, graphite, fullerenes, and carbon nanohorns is preferred, with carbon nanotubes (CNT) being particularly preferred. Note that the dispersed substance can be one of the above, or a combination of two or more.

The content of the dispersed substance in the dispersion composition may be greater than 0% by mass, relative to the total amount of the dispersion composition, but is preferably 0.0001% by mass or more, more preferably 0.001% by mass or more, and even more preferably 0.003% by mass or more. Furthermore, from the perspective of suppressing aggregation of the dispersed substance due to an excess amount of the dispersed substance, the content of the dispersed substance is preferably 0.05% by mass or less, more preferably 0.02% by mass or less, and even more preferably 0.01% by mass or less, relative to the total amount of the dispersion composition.

<(B) Dispersion medium>
The dispersion medium is a phase in which the substance to be dispersed is dispersed, and is preferably an organic solvent. The organic solvent is not particularly limited, and examples thereof include aprotic polar solvents, phenolic solvents, ketone solvents, ether solvents, ester solvents, alcohol solvents, halogenated hydrocarbon solvents, and hydrocarbon solvents.

Specific examples of these include aprotic polar solvents such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1,3-dimethyl-1-imidazolidinone, γ-butyrolactone, γ-butyrolactam, N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, N,N,2-trimethylpropanamide, acetonitrile, dimethyl sulfoxide, tetramethylurea, and hexamethylphosphortriamide;
Phenol solvents such as m-cresol, xylenol, and halogenated phenols;
Examples of ketone solvents include cyclobutanone, cyclopentanone, cyclohexanone, cycloheptanone, acetone, methyl ethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, diethyl ketone, di-n-butyl ketone, methyl i-butyl ketone, methyl n-pentyl ketone, ethyl n-butyl ketone, methyl n-hexyl ketone, diisobutyl ketone, and trimethylnonanone;
Examples of ether solvents include partial ethers of polyhydric alcohols such as propylene glycol monomethyl ether (PGME), diethylene glycol diethyl ether (DEDG), diethylene glycol ethyl methyl ether, 3-methoxy-1-butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol-n-propyl ether, ethylene glycol-i-propyl ether, ethylene glycol-n-butyl ether (butyl cellosolve), 1-butoxy-2-propanol, ethylene glycol dimethyl ether, ethylene glycol ethyl ether acetate, diethylene glycol dimethyl ether, and dipropylene glycol monomethyl ether; partial esters of polyhydric alcohols such as diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate (PGMEA), and propylene glycol monoethyl ether acetate; and cyclic ethers such as tetrahydrofuran.
Examples of ester solvents include methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, i-butyl acetate, sec-butyl acetate, t-butyl acetate, 3-methoxybutyl acetate, methyl acetoacetate, ethyl acetoacetate, ethyl propionate, butyl propionate, methyl lactate, ethyl lactate, butyl lactate, ethylene carbonate, and propylene carbonate;
Examples of alcohol solvents include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, 1-pentanol, 3-methyl-1-butanol, 1-hexanol, 2-hexanol, heptanol, cyclohexanol, methylcyclohexanol, diacetone alcohol, propane-1,2-diol, and ethylene glycol;
Halogenated hydrocarbon solvents such as dichloromethane, 1,2-dichloroethane, 1,4-dichlorobutane, and trichloroethane;
Examples of hydrocarbon solvents include hexane, heptane, octane, benzene, toluene, xylene, etc. As the dispersion medium, one type may be used alone, or two or more types may be used in combination.

Among the above, aprotic polar solvents are preferred because they have high solubility for polyamic acid and can provide excellent dispersibility and dispersion stability for the dispersed material. In particular, at least one compound selected from the group consisting of N-methylpyrrolidone, N-ethylpyrrolidone, and γ-butyrolactone (hereinafter also referred to as the "specific solvent") is preferred. The proportion of the aprotic polar solvent in the dispersion composition is preferably greater than 50% by mass, more preferably 70% by mass or more, even more preferably 85% by mass or more, and particularly preferably 95% by mass or more, based on the total amount of dispersion medium contained in the dispersion composition. The content of the specific solvent (total amount when two or more types are contained) is preferably 50% by mass or more, more preferably 65% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the total amount of dispersion medium contained in the dispersion composition.

<(C) Polyamic Acid>
The dispersion composition of the present disclosure contains a polyamic acid (hereinafter also referred to as polyamic acid [P]). The polyamic acid [P] functions as a dispersant. The polyamic acid [P] has at least one structure (hereinafter also referred to as a "specific structure") selected from the group consisting of a steroid structure and a structure represented by the following formula (1):
*-L ¹ -R ¹ -R ² -R ³ -R ⁴ ...(1)
(In formula (1), L ¹ is a single bond, —O—, —CO—, —COO-* ¹ , —OCO-* ¹ , —NR ⁵ —, —NR ⁵ —CO-* ¹ , —CO-NR ⁵ —* ¹ , an alkanediyl group having 1 to 6 carbon atoms, —O-R ⁶ —* ¹ , or —R ⁶ —O-* ¹ (wherein R ⁵ is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms, and R ⁶ is an alkanediyl group having 1 to 3 carbon atoms. * ¹ is a bond to R ¹ ). R ¹ and R ³ are each independently a single bond, a substituted or unsubstituted phenylene group, or a substituted or unsubstituted cycloalkylene group. ^{R 2} is a single bond, a substituted or unsubstituted phenylene group, a substituted or unsubstituted cycloalkylene group, or —R ⁷ -B ¹ -R ⁸ - (wherein R ⁷ and R ⁸ are each independently a substituted or unsubstituted phenylene group or a substituted or unsubstituted cycloalkylene group, and B ¹ is a single bond, —O—, —COO-* ² , —OCO-* ² , —OCH ₂ -* ² , —CH ₂ O-* ² , or an alkanediyl group having 1 to 3 carbon atoms. * ² is a bond to R ⁸ ). R ⁴ is a hydrogen atom, a fluorine atom, a cyano group, * ³ -OCO-CH ₃ (* ³ is R is a bond to ^3. ), an alkyl group having 1 to 18 carbon atoms, a fluoroalkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, a fluoroalkoxy group having 1 to 18 carbon atoms, or a monovalent group in which at least one hydrogen atom of an alkyl group having 1 to 18 carbon atoms has been substituted with a cyano group. However, when all of R ¹ , R ² and R ³ are single bonds, or the total number of benzene rings and cycloalkane rings possessed by R ¹ , R ² and R ³ is 1, R ⁴ is an alkyl group having 3 to 18 carbon atoms, a fluoroalkyl group having 3 to 18 carbon atoms, an alkoxy group having 3 to 18 carbon atoms, or a fluoroalkoxy group having 3 to 18 carbon atoms. * is a bond.)

A steroid structure generally has a sterane (i.e., cyclopentanoperhydrophenanthrene) skeleton with a substituent such as an alkyl group attached thereto. When the specific structure is a steroid structure, preferred examples thereof include structures having a cholestane skeleton, a cholestene skeleton, and a lanostane skeleton. The steroid structure may be a structure in which a linking group (e.g., a group other than a single bond represented by ^L1 in the above formula (1)) is linked to the skeleton. In the steroid structure, it is preferable that the portion other than the linking group is a structure consisting only of hydrogen atoms and carbon atoms (i.e., a hydrocarbon group).

When the specific structure is represented by formula (1) above, in the substituted phenylene group and substituted cycloalkylene group in formula (1), the substituent bonded to the ring is preferably an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorine atom, or a cyano group. The number of substituents each of the substituted phenylene group and substituted cycloalkylene group preferably is one or two, more preferably one. Furthermore, the substituted or unsubstituted phenylene group and substituted or unsubstituted cycloalkylene group in formula (1) may preferably be an unsubstituted phenylene group and an unsubstituted cycloalkylene group. The cycloalkylene group is a cycloalkanediyl group. The cycloalkylene group in formula (1) is preferably a cyclohexylene group (i.e., a cyclohexanediyl group), more preferably a cyclohexane-1,4-diyl group. The phenylene group (i.e., a benzenediyl group) in formula (1) is preferably a benzene-1,4-diyl group.

When ^R4 is an alkyl group having 1 to 18 carbon atoms, a fluoroalkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, a fluoroalkoxy group having 1 to 18 carbon atoms, or a monovalent group in which at least one hydrogen atom of an alkyl group having 1 to 18 carbon atoms has been substituted with a cyano group, ^R4 is preferably linear. The number of carbon atoms is preferably 2 or more, more preferably 3 or more, and even more preferably 5 or more.

When all of R ¹ , R ² and R ³ are single bonds, or the total number of benzene rings and cycloalkane rings possessed by R ¹ , R ² and R ³ is 1, R ⁴ preferably has 4 or more carbon atoms, more preferably 7 or more carbon atoms, and even more preferably 10 or more carbon atoms, in order to improve the dispersibility and dispersion stability of the dispersed substance.

The structure represented by the above formula (1) preferably has a ring structure from the viewpoint of further increasing the dispersibility and dispersion stability of the dispersed substance. Specifically, the total number of benzene rings and cycloalkane rings possessed by R ¹ , R ² and R ³ is preferably 1 or more, more preferably 1 to 4, and even more preferably 2 to 4. In formula (1), -R ¹ -R ² -R ³ -R ⁴ may preferably be a hydrocarbon group.

From the viewpoint of further improving the dispersibility and dispersion stability of the dispersed substance, the polyamic acid [P] preferably has, as the specific structure, at least one selected from the group consisting of a structure in which the total number of benzene rings and cycloalkane rings possessed by R ¹ , R ² and R ³ in the above formula (1) is 2 or more, and a steroid structure, and it is particularly preferable that the polyamic acid [P] has at least a steroid structure.

In the polyamic acid [P], the specific structure is preferably bonded to an aromatic ring such as a benzene ring. The number of carbon atoms in the specific structure is, for example, 3 to 50, preferably 5 to 40, more preferably 8 to 36, and even more preferably 12 or more, 16 or more, or 20 or more. In addition, the specific structure may preferably be composed only of carbon atoms, hydrogen atoms, and oxygen atoms, or may preferably be composed only of carbon atoms and hydrogen atoms. In some cases, the specific structure may preferably be composed of a linking group containing an oxygen atom (for example, a group other than the single bond and alkanediyl group represented by ^L1 above) and a hydrocarbon group.

Polyamic acid [P] has an amic acid structure within the molecule. There are no particular limitations on the method for synthesizing polyamic acid [P]. For example, polyamic acid [P] can be synthesized by reacting a tetracarboxylic dianhydride with a diamine compound, using a diamine compound with a specific structure such as a steroid structure.

(Synthesis of polyamic acid [P])
Tetracarboxylic acid dianhydride The tetracarboxylic acid dianhydride used in the synthesis of the polyamic acid [P] is not particularly limited, and examples thereof include aliphatic tetracarboxylic acid dianhydrides, alicyclic tetracarboxylic acid dianhydrides, and aromatic tetracarboxylic acid dianhydrides.

Specific examples of the tetracarboxylic dianhydride include aliphatic tetracarboxylic dianhydrides such as butanetetracarboxylic dianhydride and ethylenediaminetetraacetic dianhydride;
Examples of alicyclic tetracarboxylic dianhydrides include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic dianhydride, 5-(2,5-dioxotetrahydrofuran-3-yl)-3a,4,5,9b-tetrahydronaphtho[1,2-c]furan-1,3-dione, 5-(2,5-dioxotetrahydrofuran-3-yl)-8-methyl-3a,4,5,9b-tetrahydronaphtho[1,2-c]furan-1,3-dione, 3-oxabicyclo[3.2 1]octane-2,4-dione-6-spiro-3'-(tetrahydrofuran-2',5'-dione), 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 3,5,6-tricarboxy-2-carboxymethylnorbornane-2:3,5:6-dianhydride, bicyclo[3.3.0]octane-2,4,6,8-tetracarboxylic acid 2:4,6:8-dianhydride, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid 2:3,5:6-dianhydride, 4,9-dioxatricyclo[5.3.1.0]octane-2,4,6,8-tetracarboxylic acid 2:4,6:8-dianhydride, ^2,6 ]undecane-3,5,8,10-tetraone, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, etc.;
Examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 4,4'-biphthalic dianhydride, 4,4'-carbonyldiphthalic dianhydride, 4,4'-oxydiphthalic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, naphthalene-1,4,5,6-tetracarboxylic dianhydride, ethylene glycol bis(anhydrotrimellitate), and 1,3-propylene glycol bis(anhydrotrimellitate);
In addition, as the tetracarboxylic dianhydride, the tetracarboxylic dianhydrides described in JP-A-2010-97188 can be used.

The tetracarboxylic acid dianhydride used in the synthesis of polyamic acid [P] preferably contains an alicyclic tetracarboxylic acid dianhydride, as this improves the solubility of polyamic acid [P] in the dispersion medium and enhances the dispersibility and dispersion stability of the dispersed material. In the synthesis of polyamic acid [P], the ratio of the alicyclic tetracarboxylic acid dianhydride to the total amount of tetracarboxylic acid dianhydrides used (i.e., the ratio of structural units derived from alicyclic tetracarboxylic acid dianhydrides (also referred to as "structural units UA") to the total amount of structural units derived from tetracarboxylic acid dianhydrides constituting polyamic acid [P]) may be, for example, 1 mol% or more, but is preferably 5 mol% or more, more preferably 15 mol% or more, even more preferably 25 mol% or more, and particularly preferably 50 mol% or more. This ratio may be 100 mol% or less, or may be 99 mol% or less.

Of the above, the alicyclic tetracarboxylic acid dianhydride used in the synthesis of polyamic acid [P] is preferably at least one selected from the group consisting of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, bicyclo[3.3.0]octane-2,4,6,8-tetracarboxylic acid 2:4,6:8-dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, and 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride. Furthermore, the tetracarboxylic acid dianhydride may be used alone or in combination of two or more.

Diamine Compound The diamine compound used in the synthesis of the polyamic acid [P] preferably contains a diamine having the above-described specific structure (hereinafter also referred to as the "specific diamine"). A polymerization method using a specific diamine is preferred in that it facilitates the synthesis of a polyamic acid having the above-described specific structure and makes it easy to adjust the content of the above-described specific structure in one molecule of the polyamic acid. Polymerization of a monomer containing the specific diamine provides a partially imidized product having a structural unit derived from the specific diamine (hereinafter also referred to as the "structural unit UD") as the polyamic acid [P].

The specific diamine may be any of an aliphatic diamine, an alicyclic diamine, and an aromatic diamine as long as it has the above-described specific structure. From the viewpoint of further improving the dispersibility and dispersion stability of the dispersed substance, the specific diamine is preferably an aromatic diamine, and more preferably at least one selected from the group consisting of compounds represented by the following formula (2) and compounds represented by the following formula (3):

In formula (2), ^L2 is a single bond, —O—, —CO—, —COO-* ⁴ , —OCO-* ⁴ , —NR ¹⁰ —, —NR ¹⁰ -CO-* ⁴ , or —CO—NR ¹⁰ -* ⁴ (wherein R ¹⁰ is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms, and * ⁴ is a bond to R ⁹ ). R ⁹ is a monovalent group having a steroid skeleton.

(In formula (3), L ¹ , R ¹ , R ² , R ³ and R ⁴ have the same meanings as in formula (1) above.)

"-L ² -R ⁹ " in the above formula (2) and "-L ¹ -R ¹ -R ² -R ³ -R ⁴ " in the above formula (3) are specific structures.

Specific examples of the specific diamine include compounds represented by the above formula (2), such as cholestanyloxy-3,5-diaminobenzene, cholesteryloxy-3,5-diaminobenzene, cholestanyloxy-2,4-diaminobenzene, cholesteryloxy-2,4-diaminobenzene, cholestanyl 3,5-diaminobenzoate, cholesteryl 3,5-diaminobenzoate, lanostannyl 3,5-diaminobenzoate, 3,6-bis(4-aminobenzoyloxy)cholestane, and 3,6-bis(4-aminophenoxy)cholestane;
Examples of the compound represented by the above formula (3) include butanoxy-2,4-diaminobenzene, butanoxy-3,5-diaminobenzene, pentanoxy-2,4-diaminobenzene, pentanoxy-3,5-diaminobenzene, hexanoxy-3,5-diaminobenzene, heptanoxy-2,4-diaminobenzene, dodecanoxy-2,4-diaminobenzene, pentadecanoxy-2,4-diaminobenzene, hexadecanoxy-2,4-diaminobenzene, octadecanoxy-2,4-diaminobenzene, pentadecanoxy-2,5-diaminobenzene, octadecanoxy-2,5-diaminobenzene, 4-(4'-trifluoromethoxybenzoyloxy)cyclohexyl-3,5-diaminobenzoate, and compounds represented by the following formula (E-1):

(In formula (E-1), X ^I and X ^II are each independently a single bond, —O—, *-COO—, or *-OCO— (where * represents a bond to X ^I ), R ^I is an alkanediyl group having 1 to 3 carbon atoms, R ^II is a single bond or an alkanediyl group having 1 to 3 carbon atoms, R ¹¹ is a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a fluoroalkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, or a fluoroalkoxy group having 1 to 18 carbon atoms, a is an integer of 0 to 2, b is an integer of 0 to 2, and d is 0 or 1, provided that a and b are not 0 at the same time.)

Specific examples of the compound represented by formula (E-1) above include compounds represented by the following formulas (E-1-1) to (E-1-13).

(In formulas (E-1-1) to (E-1-13), X ¹ represents —O—, —OCH ₂ —, —CH ₂ O—, —COO—CH ₂ —, or —CH ₂ —OCO—; R ¹¹ has the same meaning as in formula (E-1); and R ¹² represents an alkyl group having 3 to 18 carbon atoms, a fluoroalkyl group having 3 to 18 carbon atoms, an alkoxy group having 3 to 18 carbon atoms, or a fluoroalkoxy group having 3 to 18 carbon atoms.)

In the polyamic acid [P], the content of the structural unit UD derived from a specific diamine is preferably 1 mol% or more relative to the total amount of structural units derived from diamines constituting the polyamic acid [P]. A content of the structural unit UD of 1 mol% or more is advantageous in that the introduction of the specific structure can sufficiently improve the dispersibility and dispersion stability of the dispersed substance. From this perspective, the content of the structural unit UD is preferably 2 mol% or more, more preferably 5 mol% or more, and even more preferably 10 mol% or more, 15 mol% or more, or 20 mol% or more relative to the total amount of structural units derived from diamines constituting the polyamic acid [P]. Furthermore, from the perspective of suppressing a decrease in the solubility of the polyamic acid [P] in the dispersion medium, the content of the structural unit UD is preferably 95 mol% or less, more preferably 90 mol% or less, and even more preferably 80 mol% or less relative to the total amount of structural units derived from diamines constituting the polyamic acid [P]. In the synthesis of the polyamic acid [P], the specific diamine may be used alone or in combination of two or more.

When synthesizing polyamic acid [P], only the specific diamine may be used as the diamine compound, but diamines not having the specific structure (hereinafter also referred to as "other diamines") may also be used together with the specific diamine. As the other diamine, a diamine having neither an anionic functional group nor a cationic functional group is preferred, from the viewpoint of not impairing the solubility of polyamic acid [P] in organic solvents. Furthermore, from the viewpoint of further improving the dispersibility and dispersion stability of the dispersed substance, the other diamine is preferably an aromatic diamine.

Specific examples of other diamines include aliphatic diamines such as metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, and 1,3-bis(aminomethyl)cyclohexane;
Alicyclic diamines such as 1,4-diaminocyclohexane and 4,4′-methylenebis(cyclohexylamine);
Examples of aromatic diamines include paraphenylenediamine, metaphenylenediamine, 4,4'-diaminodiphenylmethane, 4-aminophenyl-4'-aminobenzoate, 4,4'-diaminobenzanilide, 4,4'-diaminodiphenylamine, 4,4'-diaminoazobenzene, 1,5-bis(4-aminophenoxy)pentane, 1,7-bis(4-aminophenoxy)heptane, bis[2-(4-aminophenyl)ethyl]hexanedioic acid, N,N-bis(4-aminophenyl)methylamine, 1,5-diaminonaphthalene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,7-diaminofluorene, 4,4'-diamino Main chain diamines such as diphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-(p-phenylenediisopropylidene)bisaniline, 4,4'-(m-phenylenediisopropylidene)bisaniline, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-[4,4'-propane-1,3-diylbis(piperidine-1,4-diyl)]dianiline, 1,4-bis(4-aminophenyl)piperazine, and 1,4-bis(4-amino(3-pyridinyl))piperazine;
Examples of diaminoorganosiloxanes include 1,3-bis(3-aminopropyl)-tetramethyldisiloxane, etc. In addition, diamines described in JP-A-2010-97188 can also be used.

In the polyamic acid [P], the content of structural units derived from other diamines (hereinafter also referred to as "structural units UE") is preferably 99 mol% or less, more preferably 98 mol% or less, and even more preferably 95 mol% or less, based on the total amount of structural units derived from diamines constituting the polyamic acid. Furthermore, the content of structural units UE is preferably 5 mol% or more, more preferably 10 mol% or more, and even more preferably 20 mol% or more, based on the total amount of structural units derived from diamines constituting the polyamic acid. When synthesizing the polyamic acid, one type of other diamine may be used alone, or two or more types may be used in combination.

The polyamic acid [P] may be a copolymer essentially consisting of a tetracarboxylic dianhydride and a diamine compound. In the polyamic acid [P], the molar ratio of the structural units derived from the tetracarboxylic dianhydride to the structural units derived from the diamine compound is preferably in the range of 40:60 to 60:40, and more preferably in the range of 45:55 to 55:45. Furthermore, the total content of the structural units derived from the tetracarboxylic dianhydride and the structural units derived from the diamine compound relative to the total structural units contained in the polyamic acid [P] is preferably 70 mol% or more, more preferably 80 mol% or more, 90 mol% or more, or 95 mol% or more.

Polyamic acid [P] can be obtained by reacting the above-mentioned tetracarboxylic dianhydride with a diamine compound, optionally with a molecular weight modifier. The ratio of tetracarboxylic dianhydride and diamine compound used in the synthesis reaction of polyamic acid [P] is preferably such that 0.2 to 2 equivalents of acid anhydride groups of the tetracarboxylic dianhydride are used per equivalent of amino groups of the diamine compound, more preferably 0.3 to 1.4 equivalents, even more preferably 0.6 to 1.2 equivalents, and even more preferably 0.8 to 1.1 equivalents.

Examples of molecular weight modifiers include acid monoanhydrides such as maleic anhydride, phthalic anhydride, and itaconic anhydride; monoamine compounds such as aniline, cyclohexylamine, and n-butylamine; and monoisocyanate compounds such as phenyl isocyanate and naphthyl isocyanate. The proportion of molecular weight modifier used is preferably 20 parts by weight or less, and more preferably 10 parts by weight or less, per 100 parts by weight of the total of the tetracarboxylic dianhydride and diamine compounds used.

The synthesis reaction of polyamic acid [P] is preferably carried out in an organic solvent. The reaction temperature is preferably -20°C to 150°C, more preferably 0°C to 100°C. The reaction time is preferably 0.1 to 24 hours, more preferably 0.5 to 12 hours.

Examples of organic solvents used in the reaction include aprotic polar solvents, phenolic solvents, alcohols, ketones, esters, ethers, halogenated hydrocarbons, and hydrocarbons. Among these organic solvents, it is preferable to use one or more selected from the group consisting of aprotic polar solvents and phenolic solvents (Group 1 organic solvents), or a mixture of one or more selected from Group 1 organic solvents with one or more selected from the group consisting of alcohols, ketones, esters, ethers, halogenated hydrocarbons, and hydrocarbons (Group 2 organic solvents). In the latter case, the proportion of Group 2 organic solvent used is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total amount of Group 1 organic solvents and Group 2 organic solvents.

Particularly preferred organic solvents are one or more selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, tetramethylurea, hexamethylphosphortriamide, m-cresol, xylenol, and halogenated phenols. It is preferable to use one or more of these as the solvent, or a mixture of one or more of these with other organic solvents in the above-mentioned proportions. The amount of organic solvent (a) used is preferably an amount such that the total amount (b) of tetracarboxylic dianhydride and diamine is 0.1 to 50% by mass relative to the total amount (a + b) of the reaction solution.

The polyamic acid [P] obtained in this manner preferably has a solution viscosity of 10 to 2,000 mPa·s when made into a 10% by weight solution, and more preferably 20 to 1,000 mPa·s. The solution viscosity (mPa·s) of the polyamic acid is a value measured at 25°C using an E-type rotational viscometer for a 10% by weight solution prepared using a good solvent for the polyamic acid (e.g., N-methyl-2-pyrrolidone or γ-butyrolactone).

The polystyrene-equivalent weight average molecular weight (Mw) of the polyamic acid [P] measured by gel permeation chromatography (GPC) is preferably 1,000 to 500,000, and more preferably 2,000 to 300,000. Furthermore, the molecular weight distribution (Mw/Mn), expressed as the ratio of Mw to the polystyrene-equivalent number average molecular weight (Mn) measured by GPC, is preferably 15 or less, and more preferably 10 or less.

Here, carbon nanotubes, which are one of the dispersed substances, have excellent properties such as electrical conductivity, heat resistance, toughness, and lightweight. However, carbon nanotubes have a high tendency to aggregate, making them difficult to disperse uniformly in a dispersion medium. Furthermore, if the carbon nanotubes are not well dispersed, there is a concern that the various properties of the carbon nanotubes (e.g., electrical conductivity and resistance to external forces) may not be fully exhibited in films, wiring, etc. obtained using the dispersion composition. In this regard, the dispersion composition of the present disclosure contains polyamic acid [P], which provides excellent dispersibility of carbon nanotubes in dispersion media (e.g., organic solvents). Furthermore, by using a dispersion composition containing carbon nanotubes and polyamic acid [P], it is possible to form films, etc. that have excellent dispersant removal properties and excellent electrical properties.

The content of polyamic acid [P] in the dispersion composition is selected appropriately taking into consideration the type of material to be dispersed, but is preferably 5,000 parts by mass or more, and more preferably 10,000 parts by mass or more, per 100 parts by mass of the material to be dispersed. Furthermore, the content of polyamic acid [P] is preferably 100,000 parts by mass or less, more preferably 50,000 parts by mass or less, and even more preferably 20,000 parts by mass or less, per 100 parts by mass of the material to be dispersed.

More specifically, for example, when the dispersed substance is carbon nanotubes, from the viewpoint of sufficiently increasing the dispersibility of the carbon nanotubes, the content of polyamic acid [P] is preferably 5,000 parts by mass or more, and more preferably 10,000 parts by mass or more, per 100 parts by mass of carbon nanotubes. Furthermore, the content of polyamic acid [P] is preferably 100,000 parts by mass or less, more preferably 50,000 parts by mass or less, and even more preferably 20,000 parts by mass or less, per 100 parts by mass of carbon nanotubes.

It is not clear why the incorporation of polyamic acid [P] into the dispersion composition improves the dispersibility and dispersion stability of the dispersed substance. One hypothesis is that the excluded volume effect of the specific structure of polyamic acid [P] inhibits aggregation of the dispersed substance, and that the electrostatic interaction of polyamic acid improves the dispersion stability of the dispersed substance.

<Other ingredients>
The dispersion composition of the present disclosure may contain other components in addition to the dispersed substance, dispersion medium, and polyamic acid [P], as long as the purpose and effects of the present disclosure are not impaired. Examples of other components include dispersants other than the polyamic acid [P] (hereinafter also referred to as "other dispersants"), surfactants, fillers, antifoaming agents, sensitizers, antioxidants, adhesion aids, antistatic agents, leveling agents, antibacterial agents, etc. The content ratio of other components can be appropriately set depending on each compound to be blended, as long as the effects of the present disclosure are not impaired.

In addition, when the dispersion composition of the present disclosure contains other dispersants, the content of the other dispersants is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the total amount of polyamic acid [P] and other dispersants contained in the dispersion composition.

The method for preparing the dispersion composition is not particularly limited and can be carried out according to known methods. For example, the dispersion composition can be prepared by mixing the substance to be dispersed, the dispersion medium, and the dispersant, and then heating, stirring, etc. as necessary. The temperature when preparing the dispersion composition is preferably 5 to 90°C, and more preferably 10 to 65°C. The process of mixing the substance to be dispersed, the dispersion medium, and the dispersant may be carried out using a homogenizer, bead mill, etc.

The solids concentration of the dispersion composition (i.e., the proportion of the total mass of the dispersion composition's components other than the dispersion medium) is selected appropriately, taking into consideration factors such as viscosity and the volatility of the dispersion medium. For example, when the dispersed substance is carbon such as carbon nanotubes, the solids concentration is preferably in the range of 0.1 to 10.0% by mass, more preferably 0.3 to 6.0% by mass, and even more preferably 0.5 to 2.0% by mass.

The dispersion composition of the present disclosure uses polyamic acid [P] as a polymer dispersant. This suppresses aggregation of the dispersed substance in the dispersion medium, allowing the dispersed substance to be uniformly dispersed. By applying the dispersion composition of the present disclosure to a substrate and then removing the dispersion medium, preferably by heating, a thin film containing the dispersed substance can be formed on the substrate. The dispersion composition of the present disclosure can also be used in liquid form, either as is or by mixing it with other dispersions.

The dispersion composition and dispersant disclosed herein can be used in a variety of applications depending on the type of dispersed material. Specifically, they can be used in transparent conductive films, antistatic films, insulating films, protective films, antireflective films, colored films, field-effect transistors (FETs), touch panels, conductive inks, paints, printing inks, inkjet coating inks, etc.

The following examples provide a more detailed explanation, but the present invention is not limited to these examples. In the following examples, the weight-average molecular weight Mw of the polymer and the solution viscosity of the polymer solution were measured using the following methods. The required amounts of the raw material compounds and polymers used in the following examples were obtained by repeating synthesis on the synthesis scale shown in the synthesis examples below as necessary.

1. Polymer Synthesis [Synthesis Example 1: Synthesis of Polyamic Acid]
33.4 g (95 parts by mole) of 2,3,5-tricarboxycyclopentylacetic dianhydride (AN-2), 16.4 g (20 parts by mole) of cholestanyl 3,5-diaminobenzoate (DA-1), and 25.1 g (80 parts by mole) of 4,4'-diaminodiphenyl ether (DA-6) were dissolved in 425 g of N-methyl-2-pyrrolidone (NMP), and the reaction was carried out at room temperature for 6 hours. The reaction mixture was poured into a large excess of methanol to precipitate the reaction product. This precipitate was washed with methanol and dried under reduced pressure at 40°C for 15 hours, yielding 67 g of polyamic acid (hereinafter referred to as "polymer (paa-1)").

[Synthesis Examples 2 to 10, Comparative Synthesis Examples 1 and 2]
Polyamic acids (polymers (paa-2) to (paa-12)) were obtained in the same manner as in Synthesis Example 1, except that the types and amounts of the tetracarboxylic dianhydride and diamine compound used in the reaction were changed as shown in Table 1 below. Note that (paa-11) and (paa-12) obtained in Comparative Synthesis Example 1 and Comparative Synthesis Example 2 are polyamic acids that do not have a steroid structure or a structure represented by formula (1). Each polyamic acid is shown in Table 1 below.

Comparative Example 3: Synthesis of Polyimide
Similar to Synthesis Example 1, 95 mol parts of 2,3,5-tricarboxycyclopentylacetic dianhydride (AN-2), 20 mol parts of cholestanyl 3,5-diaminobenzoate (DA-1), and 80 mol parts of 4,4'-diaminodiphenyl ether (DA-6) were dissolved in N-methyl-2-pyrrolidone (NMP) to obtain a polyamic acid solution with a polymer concentration of 15% by mass. NMP was added to the resulting polyamic acid solution to dilute it to a polymer concentration of 10% by mass, after which predetermined amounts of pyridine and acetic anhydride were added and the mixture was reacted at 110°C for 4 hours. The resulting reaction mixture was then poured into a large excess of methanol to precipitate the reaction product. The recovered precipitate was washed with methanol and then dried under reduced pressure at 100°C to obtain a polyimide (hereinafter referred to as "polymer (PI-1)"). The imidization rate of the resulting polymer (PI-1) was 50%.

The numerical values in Table 1 indicate the proportion (mol %) of tetracarboxylic dianhydrides used relative to the total amount of tetracarboxylic dianhydrides used in the reaction, and the numerical values in Table 1 indicate the proportion (mol %) of diamine compounds used relative to the total amount of diamine compounds used in the reaction. The molar ratio of all tetracarboxylic dianhydrides to all diamine compounds used in each Synthesis Example and Comparative Example was 95:100. The abbreviations for the tetracarboxylic dianhydrides and diamine compounds in Table 1 are as follows:
(Tetracarboxylic acid dianhydride)
AN-1: Bicyclo[3.3.0]octane-2,4,6,8-tetracarboxylic acid 2:4,6:8-dianhydride AN-2: 2,3,5-tricarboxycyclopentylacetic acid dianhydride AN-3: Pyromellitic dianhydride (diamine compound)
DA-1; cholestanyl 3,5-diaminobenzoate DA-2; cholestanyloxy-2,4-diaminobenzene DA-3; a compound represented by the following formula (DA-3) DA-4; a compound represented by the following formula (DA-4) DA-5; paraphenylenediamine DA-6; 4,4'-diaminodiphenyl ether DA-7; a compound represented by the following formula (DA-7) DA-8; a compound represented by the following formula (DA-8)

2. Preparation and Evaluation of Dispersion Composition [Example 1]
(1) Preparation of Dispersion Composition To a vessel containing 10 parts by mass of single-walled carbon nanotubes (SWNTs) as a dispersion medium and 500 parts by mass of the polymer (paa-1) obtained in Synthesis Example 1 as a dispersant, NMP was added as a dispersion medium to make the total amount 100,000 parts by mass. Next, ultrasonic dispersion was carried out for 60 minutes to prepare a dispersion composition (S-1).

(2) Evaluation of Dispersibility The dispersion composition (S-1) obtained in (1) above was placed on a flat surface in an environment of 25 ° C. The evaluation was as follows: if the CNT, which is the dispersed substance, maintained its initial dispersion state without settling after one week, it was rated "best (A ⁺⁺ )"; if the CNT maintained its initial dispersion state without settling after three days, it was rated "excellent (A ⁺ )"; if the CNT maintained its initial dispersion state without settling after one day, it was rated "good (A)"; if the CNT maintained its initial dispersion state without settling after three hours, it was rated "fair (B)"; if settling or aggregation of CNT was observed within three hours, it was rated "poor (C)". As a result, the dispersibility of this dispersion composition (S-1) was rated "best (A ⁺⁺ )".

(3) Evaluation of Dispersion Stability (Durability) A dispersion composition was prepared in the same manner as in (1) above. The obtained dispersion composition was left to stand on a flat surface in an environment of 40 ° C., and the dispersion state over time was observed. The evaluation was as follows: if the CNT did not settle after one week and maintained its initial dispersion state, it was rated "best (A ⁺⁺ )"; if the CNT did not settle after three days and maintained its initial dispersion state, it was rated "excellent (A ⁺ )"; if the CNT did not settle after one day and maintained its initial dispersion state, it was rated "good (A)"; if the CNT did not settle after three hours and maintained its initial dispersion state, it was rated "fair (B)"; and if sedimentation or aggregation was observed after three hours, it was rated "poor (C)". As a result, the dispersion stability of this dispersion composition (S-1) was rated "best (A ⁺⁺ )".

(4) Evaluation of Coatability The dispersion composition (S-1) obtained in (1) above was applied to a glass substrate using a blade and dried on a hot plate at 80 ° C. for 10 minutes to form a coating film having a thickness of 0.1 μm at the center of the substrate. This coating film was observed under a microscope at a magnification of 50 times to check for unevenness in the coating film thickness and the presence or absence of pinholes. The evaluation was as follows: when neither unevenness in the coating thickness nor pinholes were observed, the coating property was rated "good (A)", when at least one of unevenness in the coating thickness and pinholes was slightly observed, the coating property was rated "fair (B)", and when at least one of unevenness in the coating thickness and pinholes was clearly observed, the coating property was rated "poor (C)". As a result, neither unevenness in the coating thickness nor pinholes was observed, and the coating property of this dispersion composition (S-1) was "good (A)".

(5) Evaluation of Dispersant Removability The dispersion composition (S-1) obtained in (1) above was applied to a glass substrate using a blade and dried on a hot plate at 80 ° C. for 10 minutes to form a coating film with a film thickness of 0.1 μm at the center of the substrate. This coating film was immersed in a sodium hydroxide aqueous solution for 1 minute, and the surface was observed with an AFM (atomic force microscope, manufactured by Hitachi High-Tech Corporation). Those in which the dispersant on the surface was removed and CNT exposure was observed were rated "Good (A)" (example: Figure 1), those in which CNT was partially exposed were rated "Fair (B)", and those in which the surface was covered with resin and no CNT exposure was observed, or the film formation was so poor that it could not be determined were rated "Poor (C)" (example: Figure 2). As a result, the dispersant on the surface was removed and CNT exposure was observed, and the dispersant removability of this dispersion composition (S-1) was rated "Good (A)".

[Examples 2 to 18, Comparative Examples 1 to 3]
Except for changing the composition (type and amount) of the dispersed substance and dispersant of the dispersion composition as shown in Table 2 below, dispersion compositions (S-2) to (S-18) and (sr-1) to (sr-3) were prepared in the same manner as the dispersion composition (S-1) of Example 1. In addition, various evaluations were performed in the same manner as in Example 1, except that dispersion compositions (S-2) to (S-18) and (sr-1) to (sr-3) were used instead of dispersion composition (S-1). The evaluation results of Examples 1 to 18 and Comparative Examples 1 to 3 are summarized in Table 2 below.

In Table 2, the numerical values for "amount blended" indicate parts by mass. The abbreviations for the dispersed substances are as follows:
<Dispersed element>
SWNT: Single-wall carbon nanotube

From the results in Table 2, compared to the case of using polyimide as the dispersant in Comparative Example 3 and the cases of using polyamic acid without a specific structure in Comparative Examples 1 and 2, Examples 1 to 18 were rated as excellent, excellent, good, or fair in terms of dispersibility, dispersion stability, coatability, and dispersant removability.
By using a dispersion composition with good dispersibility, dispersion stability, and dispersant removal properties, it was possible to obtain a film with good coating properties on a substrate and with carbon nanotubes exposed on the surface effectively.

Claims (9)

A dispersed material;
A dispersion medium;
and a polyamic acid having at least one specific structure selected from the group consisting of a steroid structure and a structure represented by the following formula (1) ,
the dispersed material is inorganic particles,
the dispersion medium comprises an aprotic polar solvent,
the proportion of the aprotic polar solvent is 70% by mass or more based on the total amount of the dispersion medium;
the polyamic acid has structural units UD derived from a diamine compound having the specific structure,
The dispersion composition , wherein the diamine compound is at least one selected from the group consisting of compounds represented by the following formula (2) and compounds represented by the following formula (3) :
*-L ¹ -R ¹ -R ² -R ³ -R ⁴ ...(1)
(In formula (1), L ¹ is a single bond, —O—, —CO—, —COO-* ¹ , —OCO-* ¹ , —NR ⁵ —, —NR ⁵ —CO-* ¹ , —CO-NR ⁵ —* ¹ , an alkanediyl group having 1 to 6 carbon atoms, —O-R ⁶ —* ¹ , or —R ⁶ —O-* ¹ (wherein R ⁵ is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms, and R ⁶ is an alkanediyl group having 1 to 3 carbon atoms. * ¹ is a bond to R ¹ ). R ¹ and R ³ are each independently a single bond, a substituted or unsubstituted phenylene group, or a substituted or unsubstituted cycloalkylene group. ^{R 2} is a single bond, a substituted or unsubstituted phenylene group, a substituted or unsubstituted cycloalkylene group, or —R ⁷ -B ¹ -R ⁸ - (wherein R ⁷ and R ⁸ are each independently a substituted or unsubstituted phenylene group or a substituted or unsubstituted cycloalkylene group, and B ¹ is a single bond, —O—, —COO-* ² , —OCO-* ² , —OCH ₂ -* ² , —CH ₂ O-* ² , or an alkanediyl group having 1 to 3 carbon atoms. * ² is a bond to R ⁸ ). R ⁴ is a hydrogen atom, a fluorine atom, a cyano group, * ³ -OCO-CH ₃ (* ³ is R is a bond to ^3. ), an alkyl group having 1 to 18 carbon atoms, a fluoroalkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, a fluoroalkoxy group having 1 to 18 carbon atoms, or a monovalent group in which at least one hydrogen atom of an alkyl group having 1 to 18 carbon atoms has been substituted with a cyano group. However, when all of R ¹ , R ² and R ³ are single bonds, or the total number of benzene rings and cycloalkane rings possessed by R ¹ , R ² and R ³ is 1, R ⁴ is an alkyl group having 3 to 18 carbon atoms, a fluoroalkyl group having 3 to 18 carbon atoms, an alkoxy group having 3 to 18 carbon atoms, or a fluoroalkoxy group having 3 to 18 carbon atoms. * is a bond.)
In formula (2), L2 ^is a single bond, —O—, —CO—, —COO-* ⁴ , —OCO-* ⁴ , —NR ¹⁰ —, —NR ¹⁰ -CO-* ⁴ , or —CO—NR ¹⁰ -* ⁴ (wherein R ¹⁰ is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms , and * ⁴ is a bond to R ⁹ ). R ⁹ is a monovalent group having a steroid skeleton, and the two amino groups are bonded to each other at the meta position.)
(In formula (3), L ¹ , R ¹ , R ² , R ³ and R ⁴ have the same meanings as in formula (1). The two amino groups are bonded to each other at the meta position.) 2. The dispersion composition according to claim 1, wherein the content of the structural units UD relative to the total amount of structural units derived from diamines constituting the polyamic acid is 1 mol % or more and 95 mol % or less. The dispersion composition according to claim 1 or 2, wherein the polyamic acid has structural units UA derived from an alicyclic tetracarboxylic dianhydride. The dispersion composition according to claim 3, wherein the content of the structural unit UA relative to the total amount of structural units derived from tetracarboxylic dianhydride constituting the polyamic acid is 5 mol % or more. The dispersion composition according to any one of claims 1 to 4 , wherein the dispersion medium comprises at least one selected from the group consisting of N-methylpyrrolidone, N-ethylpyrrolidone, and γ-butyrolactone. 6. The dispersion composition according to claim 1 , wherein the content of the dispersed substance is greater than 0% by mass and not more than 0.05% by mass relative to the total amount of the dispersion composition. The dispersion composition according to any one of claims 1 to 6 , wherein the substance to be dispersed is nanocarbon. The dispersion composition according to claim 7 , wherein the nanocarbon is at least one selected from the group consisting of carbon black, carbon fiber, carbon nanotube, graphite, fullerene, and carbon nanohorn. 9. The dispersion composition according to claim 1 , wherein the content of the polyamic acid is 5,000 parts by mass or more and 50,000 parts by mass or less per 100 parts by mass of the substance to be dispersed.