阅读说明：本技术 碳纳米管分散液、导电膜及导电性膜 (Carbon nanotube dispersion, conductive film, and conductive film ) 是由 吉原明彦 儿岛清茂 椋木康雄 小岛阳广 池上和志 于 2015-01-29 设计创作，主要内容包括：本发明涉及碳纳米管分散液、导电膜及导电性膜。本发明可提供稳定性优异、并且能够形成与基材的粘接性优异的导电膜的碳纳米管分散液。本发明的碳纳米管分散液包含碳纳米管(A)、含有含磺酸基单体单元和烯属不饱和脂肪族羧酸单体单元的高分子分散剂(B)、及溶剂(C),上述高分子分散剂(B)中上述烯属不饱和脂肪族羧酸单体单元的含有比例为25摩尔％以上且90摩尔％以下,上述高分子分散剂(B)中,上述含磺酸基单体单元的含有比例与上述烯属不饱和脂肪族羧酸单体单元的含有比例之比、即含磺酸基单体单元/烯属不饱和脂肪族羧酸单体单元的摩尔比为0.5以上且3以下,上述溶剂(C)包含水,并且,上述碳纳米管分散液的pH为0.1以上且小于7。(The invention relates to a carbon nanotube dispersion liquid, a conductive film and a conductive film. The present invention can provide a carbon nanotube dispersion liquid which is excellent in stability and can form a conductive film excellent in adhesion to a substrate. The carbon nanotube dispersion liquid of the present invention comprises carbon nanotubes (a), a polymer dispersant (B) containing a sulfonic acid group-containing monomer unit and an ethylenically unsaturated aliphatic carboxylic acid monomer unit, wherein the content ratio of the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B) is 25 to 90 mol%, the molar ratio of the content ratio of the sulfonic acid group-containing monomer unit to the content ratio of the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B), i.e., the molar ratio of the sulfonic acid group-containing monomer unit/the ethylenically unsaturated aliphatic carboxylic acid monomer unit, is 0.5 to 3, and a solvent (C), wherein the solvent (C) contains water, and the pH of the carbon nanotube dispersion liquid is 0.1 to 7.)

1. A carbon nanotube dispersion, comprising:

carbon nanotubes (A),

A polymer dispersant (B) comprising a sulfonic acid group-containing monomer unit and an ethylenically unsaturated aliphatic carboxylic acid monomer unit, and

a solvent (C) which is a mixture of,

the content ratio of the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B) is 25 to 90 mol%,

in the polymer dispersant (B), the ratio of the content ratio of the sulfonic acid group-containing monomer units to the content ratio of the ethylenically unsaturated aliphatic carboxylic acid monomer units, that is, the molar ratio of the sulfonic acid group-containing monomer units to the ethylenically unsaturated aliphatic carboxylic acid monomer units, is 0.5 to 3,

the solvent (C) contains water, and the pH of the carbon nanotube dispersion is 0.1 or more and less than 7.

2. The carbon nanotube dispersion liquid according to claim 1, wherein the sulfonic acid group-containing monomer unit in the polymer dispersant (B) is a monomer unit derived from an aromatic sulfonic acid or a salt thereof.

3. The carbon nanotube dispersion liquid according to claim 1 or 2, wherein the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B) is at least 1 selected from the group consisting of: acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and salts thereof.

4. The carbon nanotube dispersion liquid according to claim 1 or 2, wherein a content ratio of the sulfonic acid group-containing monomer unit in the polymer dispersant (B) is 10 mol% or more and less than 75 mol%.

5. The carbon nanotube dispersion liquid according to claim 1 or 2, wherein the carbon nanotubes (a) comprise at least one of single-wall carbon nanotubes and double-wall carbon nanotubes.

6. The carbon nanotube dispersion liquid according to claim 1 or 2, wherein the content of the polymer dispersant (B) is 50 parts by mass or more and 1000 parts by mass or less per 100 parts by mass of the carbon nanotube (a).

7. A conductive film obtained by using the carbon nanotube dispersion liquid according to any one of claims 1 to 6.

8. The conductive film according to claim 7, which has a surface resistivity of 20 Ω/□ or less.

9. A conductive film, comprising:

a base material, and

a conductive film on the substrate, wherein the conductive film is formed on the substrate,

the conductive film is the conductive film according to claim 7 or 8.

Technical Field

The invention relates to a carbon nanotube dispersion liquid, a conductive film and a conductive film.

Background

Carbon nanotubes (hereinafter also referred to as "CNTs") have been studied for various industrial applications because of their excellent properties such as electrical conductivity, thermal conductivity, and mechanical strength. For example, in view of its excellent conductivity, a technique of forming a conductive film using CNTs has been studied.

The conductive film comprising CNTs may be formed on a substrate by: for example, a carbon nanotube dispersion (hereinafter also referred to as "CNT dispersion") prepared by blending CNTs, a solvent, and a dispersant for uniformly dispersing the CNTs in the solvent is applied to a substrate, and the CNT dispersion on the substrate is dried. Further, in order to improve the performance of such a conductive film and a conductive film including a conductive film on a substrate, attempts have been made to improve a dispersant and a CNT dispersion liquid used for forming the conductive film.

For example, patent document 1 reports a transparent conductive film having specific light transmittance and surface resistivity, which has high durability, high conductivity, and excellent light transmittance, and which includes a conductive film formed of CNTs and an aromatic polymer as a dispersant, and a resin layer on the conductive film.

In addition, for example, patent document 2 reports the following: an aqueous CNT dispersion containing a dispersant such as a polysaccharide having a number average molecular weight of 1 to 15 ten thousand at a specific ratio to CNT and having a pH adjusted to a specific range is excellent in stability against high shear while maintaining high dispersibility.

Further, for example, patent document 3 reports the following: the polystyrene sulfonic acid copolymer comprises styrene sulfonic acid monomer residues represented by a specific structural formula, maleimide residues having a substituted or unsubstituted aromatic hydrocarbon group on a nitrogen atom, and other vinyl monomer residues derived from itaconic acid, fumaric acid, and the like as repeating structural units, wherein the content ratio of each residue is 30-95 mol%, 5-70 mol%, and 0-20 mol%, and has a strong ability to disperse CNT and the like in an aqueous medium.

Disclosure of Invention

Accordingly, an object of the present invention is to provide a carbon nanotube dispersion liquid which is excellent in stability and can form a conductive film excellent in adhesion to a substrate.

Another object of the present invention is to provide a conductive film having excellent adhesion to a substrate, and a conductive film provided with the conductive film.

Means for solving the problems

The present inventors have conducted intensive studies in order to achieve the above object. Further, the present inventors have found that: when dispersing CNTs in a solvent, a polymer dispersant comprising a sulfonic acid group-containing monomer unit and an ethylenically unsaturated aliphatic carboxylic acid monomer unit at a specific ratio is used as a dispersant, whereby aggregation of CNTs in a CNT dispersion is suppressed and a conductive film formed using the dispersion has excellent adhesion to a substrate. Thus, the present invention has been completed.

That is, an object of the present invention is to effectively solve the above problems, and a carbon nanotube dispersion liquid of the present invention includes a carbon nanotube (a), a polymer dispersant (B) containing a sulfonic acid group-containing monomer unit and an ethylenically unsaturated aliphatic carboxylic acid monomer unit, and a solvent (C), wherein a content ratio of the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B) is higher than 20 mol% and 90 mol% or less. As described above, if a polymer dispersant containing a sulfonic acid group-containing monomer unit and an ethylenically unsaturated aliphatic carboxylic acid monomer unit at a specific ratio is used as a dispersant for dispersing CNTs, a carbon nanotube dispersion liquid which is excellent in stability and can form a conductive film excellent in adhesion to a substrate can be provided.

In the present invention, the phrase "comprising … … monomer units" means that "structural units derived from the monomer are contained in the polymer obtained using the monomer".

In the carbon nanotube dispersion liquid of the present invention, the sulfonic acid group-containing monomer unit in the polymer dispersant (B) is preferably a monomer unit derived from an aromatic sulfonic acid or a salt thereof. When the polymer dispersant (B) contains a monomer unit derived from an aromatic sulfonic acid or a salt thereof as a sulfonic acid group-containing monomer unit, the stability of the CNT dispersion can be further improved.

In the carbon nanotube dispersion liquid of the present invention, the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B) is preferably a monomer unit derived from at least 1 selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and salts thereof. When the polymer dispersant (B) contains a monomer unit derived from any of the above monomers as an ethylenically unsaturated aliphatic carboxylic acid monomer unit, the stability of the CNT dispersion can be further improved.

In the carbon nanotube dispersion liquid of the present invention, the content ratio of the sulfonic acid group-containing monomer unit in the polymer dispersant (B) is preferably 10 mol% or more and less than 80 mol%. When the polymer dispersant (B) contains a sulfonic acid group-containing monomer unit in the above-described ratio, the stability of the CNT dispersion and the adhesion of the conductive film formed from the dispersion to the substrate can be further improved.

Further, in the carbon nanotube dispersion liquid of the present invention, it is preferable that the ratio of the content ratio of the sulfonic acid group-containing monomer unit to the content ratio of the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B) is 0.5 or more and less than 4. When the ratio of the content of the sulfonic acid group-containing monomer unit to the content of the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B) is within the above range, the stability of the CNT dispersion and the adhesion of the conductive film formed from the dispersion to the substrate can be further improved.

Further, in the carbon nanotube dispersion liquid of the present invention, it is preferable that the carbon nanotubes (a) include at least one of single-wall carbon nanotubes and double-wall carbon nanotubes. When at least one of single-walled carbon nanotubes and double-walled carbon nanotubes (hereinafter also referred to as "single-walled CNTs" or "double-walled CNTs", respectively) is used as the CNT, the conductive film formed from the CNT dispersion can have excellent electrical conductivity and mechanical properties.

In the carbon nanotube dispersion liquid of the present invention, it is preferable that the solvent (C) contains water and the pH of the carbon nanotube dispersion liquid is 0.1 to 8. When water is used as the solvent and the pH of the carbon nanotube dispersion is 0.1 or more and 8 or less, the stability of the CNT dispersion can be further improved.

Here, the carbon nanotube dispersion liquid of the present invention preferably contains the polymer dispersant (B) in an amount of 50 parts by mass or more and 1000 parts by mass or less per 100 parts by mass of the carbon nanotubes (a). When the amount of the polymer dispersant (B) blended with the CNTs is within the above range, the stability of the CNT dispersion and the adhesion of the conductive film formed from the CNT dispersion to the substrate can be further improved.

Further, the present invention is directed to effectively solve the above problems, and a conductive film of the present invention is obtained by using any of the carbon nanotube dispersions described above. When the CNT dispersion liquid of the present invention is used, a conductive film having excellent adhesion to a substrate can be provided.

Here, the conductive film of the present invention preferably has a surface resistivity of 20 Ω/□ or less. If the surface resistivity of the conductive film is within the above range, the conductive film provided with the conductive film on the substrate can be made excellent in conductivity, for example.

In addition, an object of the present invention is to effectively solve the above problems, and a conductive film of the present invention includes a substrate and a conductive film on the substrate, wherein the conductive film is any one of the conductive films described above. The conductive film provided with the conductive film of the present invention has excellent conductivity.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a carbon nanotube dispersion liquid which is excellent in stability and can form a conductive film excellent in adhesion to a substrate can be provided.

Further, according to the present invention, a conductive film having excellent adhesion to a substrate and a conductive film including the conductive film can be provided.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail.

Here, the carbon nanotube dispersion liquid of the present invention is used for forming a conductive film. The conductive film of the present invention is formed from the carbon nanotube dispersion of the present invention. The conductive film of the present invention is formed by providing the conductive film of the present invention on a substrate.

(carbon nanotube Dispersion liquid)

The carbon nanotube dispersion liquid of the present invention comprises: carbon nanotubes (A), a polymeric dispersant (B), and a solvent (C). Wherein the polymer dispersant (B) is characterized in that: contains a sulfonic acid group-containing monomer unit and contains an ethylenically unsaturated aliphatic carboxylic acid monomer unit in a specific content ratio. The carbon nanotube dispersion liquid of the present invention is excellent in stability, and a conductive film formed from the carbon nanotube dispersion liquid is excellent in adhesion to a substrate. The components contained in the CNT dispersion liquid of the present invention will be described in detail below.

In the present specification, "carbon nanotube (a)" is also referred to as "cnt (a)", and "polymer dispersant (B) containing a sulfonic acid group-containing monomer unit and an ethylenically unsaturated aliphatic carboxylic acid monomer unit" is also referred to as "polymer dispersant (B)".

< carbon nanotube (A) >

The CNTs (a) may be either single-walled carbon nanotubes or multi-walled carbon nanotubes, but preferably include at least one of single-walled carbon nanotubes and double-walled carbon nanotubes, and more preferably include single-walled carbon nanotubes, from the viewpoint of improving the electrical conductivity and mechanical properties of the conductive film formed from the CNT dispersion.

In addition, cnt (a) preferably has a peak of Radial Breathing Mode (RBM) when evaluated by raman spectroscopy. Note that, in the raman spectrum of the multiwall carbon nanotube having three or more walls, RBM is not present.

Further, the ratio (G/D ratio) of the G band peak intensity to the D band peak intensity of cnt (a) in the raman spectrum is preferably 1 or more and 20 or less. When the G/D ratio is 1 to 20, the conductivity and mechanical properties of the conductive film formed from the CNT dispersion can be sufficiently improved even when the amount of CNT (A) is small.

The ratio (3 σ/Av) of the diameter distribution (3 σ) to the average diameter (Av) of the cnts (a) is preferably greater than 0.20 and less than 0.60, more preferably greater than 0.25, and still more preferably greater than 0.50. If the CNT having a 3 σ/Av ratio of more than 0.20 and less than 0.60 is used, the conductivity and mechanical properties of the conductive film formed from the CNT dispersion can be sufficiently improved even if the blending amount of the CNT (a) is small.

The "diameter distribution (3 σ)" is a value obtained by multiplying a sample standard deviation (σ) of the diameter of the carbon nanotube by 3. The "average diameter of carbon nanotubes (Av)" and the "sample standard deviation of diameters of carbon nanotubes (σ)" can be obtained by measuring the diameters of 100 carbon nanotubes randomly selected using a transmission electron microscope.

The average diameter (Av) of the cnts (a) is preferably 0.5nm or more, more preferably 1nm or more, preferably 15nm or less, and more preferably 10nm or less. When the average diameter (Av) of the CNTs (a) is 0.5nm or more, the aggregation of the CNTs (a) can be suppressed, and the stability of the CNT dispersion can be further improved. In addition, if the average diameter (Av) of the CNTs (a) is 15nm or less, the mechanical properties of the conductive film formed from the CNT dispersion can be sufficiently improved.

The average diameter (Av) and the diameter distribution (3 σ) of the CNTs (a) can be adjusted by changing the production method and the production conditions of the CNTs, or by combining CNTs obtained by different production methods in various ways.

In addition, as the CNT (a), the following CNTs are generally used: the diameters of 100 CNTs selected at random were measured using a transmission electron microscope, and CNTs in a normal distribution were obtained by plotting the diameters on the horizontal axis and the frequency on the vertical axis and using gaussian approximation.

The specific surface area of CNT (A) before addition to solvent (C) is preferably 600m²The CNT (A) may be unopened or opened. In the case of unopened CNTs, the specific surface area is preferably 800m²A,/g or more, and preferably 1,200m²A ratio of 1,000m or less per gram²The ratio of the carbon atoms to the carbon atoms is less than g. On the other hand, in the case of the open CNT, the specific surface area is preferably 1,300m²A,/g or more, and preferably 2,500m²A total of 2,300m or less, preferably²The ratio of the carbon atoms to the carbon atoms is less than g. If the specific surface area of CNT (A) is 600m²When the ratio/g is higher than the above ratio, the conductivity and mechanical properties of the conductive film formed from the CNT dispersion can be improved.Further, if the specific surface area of the CNT (a) is within the above range, the stability of the CNT dispersion can be improved.

In the present invention, the specific surface area refers to a BET specific surface area based on nitrogen adsorption.

Further, the weight density of CNT (A) is preferably 0.002g/cm³Above and 0.2g/cm³The following. If the weight density is 0.2g/cm³Since the bonding between cnts (a) is weakened, cnts (a) can be dispersed more uniformly. Further, if the weight density is 0.002g/cm³As described above, since the integrity of the cnts (a) can be improved and scattering can be suppressed, handling becomes easy.

The cnt (a) preferably has a plurality of micropores. Among them, CNT (A) has micropores with a pore diameter of less than 2nm, and the amount of micropores present is preferably 0.40mL/g or more, more preferably 0.43mL/g or more, further preferably 0.45mL/g or more in terms of micropore volume, and the upper limit is usually about 0.65 mL/g. By providing CNTs (a) with the micropores described above, aggregation of CNTs (a) can be suppressed, dispersibility of CNTs (a) in the CNT-containing film can be improved, and a conductive film having excellent conductivity and mechanical properties can be effectively obtained. The micropore volume can be adjusted by, for example, appropriately changing the production method and production conditions of the cnt (a).

Here, the "micropore volume (Vp)" can be calculated by measuring a nitrogen adsorption isotherm of the CNT at a liquid nitrogen temperature (77K), setting a nitrogen adsorption amount at a relative pressure P/P0 of 0.19 as V, and calculating Vp of (V/22414) × (M/ρ) according to formula (I). In the formula (I), M is the molecular weight of the adsorbate (nitrogen) of 28.010, and ρ is the density of the adsorbate (nitrogen) at 77K of 0.808g/cm³. The micropore volume can be defined by, for example, "BELSORP (registered trademark) -mini" [ manufactured by BEL Japan)]Can be easily obtained.

Cnts (a) having the above properties can be efficiently produced by: for example, in a method (Super-growth method; refer to international publication No. 2006/011655) in which a raw material compound and a carrier gas are supplied onto a substrate having a catalyst layer for producing CNTs on the surface thereof (hereinafter, also referred to as "substrate for producing CNTs") and CNT is synthesized by a chemical vapor deposition method (CVD method) while a small amount of an oxidizing agent (catalyst activating substance) is present in the system, the catalytic activity of the catalyst layer for producing CNTs is dramatically improved, the catalyst layer is formed on the surface of the substrate by a wet method, and a raw material gas containing acetylene as a main component (for example, a gas containing acetylene in an amount of 50 vol% or more) is used. Hereinafter, the carbon nanotube obtained by the Super-growth method is also referred to as "SGCNT". By using SGCNT as cnt (a), the conductive film can have more excellent adhesion to the substrate.

The concentration of the CNT (a) in the CNT dispersion liquid of the present invention is not particularly limited as long as the dispersion liquid can be formed, and the concentration of the CNT in the dispersion liquid is preferably 0.005 mass% or more, more preferably 0.01 mass% or more, further preferably 0.05 mass% or more, particularly preferably 0.1 mass% or more, preferably 20 mass% or less, more preferably 10 mass% or less, and further more preferably 5 mass% or less.

The CNT dispersion liquid of the present invention has the following advantages based on the excellent contribution as a dispersant of the polymer dispersant (B) described later: compared with the conventional CNT dispersion, the stability of CNT can be ensured even if the CNT is mixed at a high concentration. Further, by including CNTs in a high concentration in the CNT dispersion, the CNT coating amount per unit area of the substrate can be increased to a desired value with a smaller number of coating times than in the case of using a conventional CNT dispersion.

< Polymer dispersant (B) >

In the CNT dispersion liquid of the present invention, a polymer dispersant containing a sulfonic acid group-containing monomer unit and containing an ethylenically unsaturated aliphatic carboxylic acid monomer unit at a specific content ratio is used as the dispersant.

By using such a polymer dispersant, aggregation of CNTs (a) in the CNT dispersion can be suppressed, and the CNT dispersion can have excellent stability. In addition, the conductive film formed from the CNT dispersion liquid containing the polymer dispersant (B) has excellent adhesion to a substrate due to contributions of both sulfonic acid groups and carboxyl groups contained in the polymer dispersant.

In general, the dispersant often becomes an impedance after the conductive film is formed, and the conductivity of the conductive film is lowered. However, since the polymer dispersant (B) used in the present invention can disperse the CNTs (a) extremely well, the CNT dispersion liquid of the present invention can provide a conductive film having excellent conductivity without being affected by the dispersant as an impedance factor.

The monomer capable of forming the monomer unit constituting the polymer dispersant (B) will be described in detail below.

[ sulfonic acid group-containing monomer ]

The sulfonic acid group-containing monomer capable of forming the sulfonic acid group-containing monomer unit of the polymer dispersant (B) is not particularly limited as long as it is a monomer having a sulfonic acid group and a group copolymerizable with other monomers such as a carbon-carbon unsaturated bond, and examples thereof include: aromatic sulfonic acids such as styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, acrylamide-t-butylsulfonic acid, and acrylamide-N-butanesulfonic acid. Here, the sulfonic acid group-containing monomer may be in the form of an inorganic salt or an organic salt in which a hydrogen atom in the sulfonic acid group is replaced with an inorganic ion or an organic ion. That is, the sulfonic acid group-containing monomer may be in the form of a sulfonate.

Examples of the inorganic salt include alkali metal salts (lithium, sodium, potassium, and the like), and examples of the organic salt include: alkylamine salts (methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, trimethylamine, tripropylamine, tributylamine, tri-tert-butylamine, etc.), arylamine salts (phenylamine, benzylamine, etc.), and the like. These sulfonic acid group-containing monomers may be used singly or in combination of two or more.

Of these, from the viewpoint of improving the stability of the CNT dispersion, the sulfonic acid group-containing monomer is preferably an aromatic sulfonic acid such as styrenesulfonic acid, vinylsulfonic acid, acrylamide-t-butylsulfonic acid, or an alkali metal salt (sodium or potassium) thereof, and more preferably styrenesulfonic acid, vinylsulfonic acid, or an alkali metal salt (sodium or potassium) thereof.

The content of the sulfonic acid group-containing monomer unit in the polymer dispersant (B) (the ratio of the sulfonic acid group-containing monomer unit to the whole monomer units) is usually 10 mol% or more and less than 80 mol%, preferably 20 mol% or more, more preferably 30 mol% or more, particularly preferably 40 mol% or more, preferably 70 mol% or less, more preferably 60 mol% or less. When the content ratio of the sulfonic acid group-containing monomer unit in the polymer dispersant (B) is within the above range, the stability of the CNT dispersion and the adhesion of the conductive film formed from the dispersion to the substrate can be improved.

[ ethylenically unsaturated aliphatic carboxylic acid monomer ]

The ethylenically unsaturated aliphatic carboxylic acid monomer that can form the ethylenically unsaturated aliphatic carboxylic acid monomer unit of the polymer dispersant (B) is not particularly limited as long as it is an aliphatic carboxylic acid having a carbon-carbon double bond that is copolymerizable with other monomers, and examples thereof include: acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and the like. Here, the ethylenically unsaturated aliphatic carboxylic acid monomer may be in the form of an inorganic salt or an organic salt in which a hydrogen atom in a carboxyl group is replaced with an inorganic ion or an organic ion. That is, the ethylenically unsaturated aliphatic carboxylic acid monomer may be in the form of a carboxylate. Here, as the inorganic salt and the organic salt, the same ones as those listed in the above item [ sulfonic acid group-containing monomer ] can be listed. These ethylenically unsaturated aliphatic carboxylic acid monomers may be used alone or in combination of two or more.

In addition, if the polymer dispersant (B) has a repeating structure derived from an ethylenically unsaturated aliphatic carboxylic acid monomer, the adhesiveness to a substrate can be greatly improved as compared with the case of having a structure derived from an ethylenically unsaturated aromatic carboxylic acid monomer (N-carboxyphenylmaleimide, 4-vinylbenzoic acid, etc.).

Further, as the ethylenically unsaturated aliphatic carboxylic acid monomer, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and salts thereof are preferable, and acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and alkali metal salts (sodium and potassium) thereof are more preferable, from the viewpoint of improving the stability of the CNT dispersion.

The content of the ethylenically unsaturated aliphatic carboxylic acid monomer unit (the ratio of the ethylenically unsaturated aliphatic carboxylic acid monomer unit to the whole monomer units) in the polymer dispersant (B) needs to be higher than 20 mol% and 90 mol% or less, preferably 25 mol% or more, more preferably 30 mol% or more, particularly preferably 40 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, and particularly preferably 60 mol% or less. When the content ratio of the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B) is 20 mol% or less, adhesiveness to the substrate cannot be ensured, and when it is more than 90 mol%, both solubility in a solvent and dispersibility of the CNT cannot be ensured.

[ molar ratio of sulfonic acid group-containing monomer to ethylenically unsaturated aliphatic carboxylic acid monomer ]

Here, in the polymer dispersant (B), the ratio of the content ratio (mol%) of the sulfonic acid group-containing monomer unit to the content ratio (mol%) of the ethylenically unsaturated aliphatic carboxylic acid monomer unit (also referred to as "sulfonic acid group-containing monomer/ethylenically unsaturated aliphatic carboxylic acid monomer mol ratio") is preferably 0.5 or more, more preferably 1 or more, preferably less than 4, and more preferably 3 or less. When the molar ratio of the sulfonic acid group-containing monomer/ethylenically unsaturated aliphatic carboxylic acid monomer is within the above range, the stability of the CNT dispersion and the adhesion of the conductive film formed from the CNT dispersion to the substrate can be improved.

[ other monomers ]

The polymer dispersant (B) may contain any repeating unit in addition to the sulfonic acid group-containing monomer unit and the ethylenically unsaturated aliphatic carboxylic acid monomer unit as described above, as long as the effect of the present invention is not significantly impaired. Examples of other monomers that can form such an arbitrary repeating unit include: acrylates (methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, benzyl acrylate, etc.), methacrylates (methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, benzyl methacrylate, etc.), itaconates (methyl itaconate, ethyl itaconate, propyl itaconate, butyl itaconate, benzyl itaconate, etc.), styrene, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, itaconamide, N-dimethylacrylamide, etc.

The content ratio of the monomer units other than the sulfonic acid group-containing monomer unit and the ethylenically unsaturated aliphatic carboxylic acid monomer unit in the polymer dispersant (B) is preferably 30 mol% or less, more preferably 20 mol% or less, still more preferably 10 mol% or less, and particularly preferably 5 mol% or less.

[ preparation of Polymer dispersant (B) ]

The polymer dispersant (B) can be produced, for example, by polymerizing a monomer composition containing the above-mentioned monomer in a reaction solvent.

Here, the content ratio of each monomer (the ratio (mol%) of the total monomers) in the monomer composition is generally the same as the desired content ratio (the ratio (mol%) of the total monomer units) of the corresponding monomer units (repeating units) in the polymeric dispersant (B).

The reaction solvent, polymerization method, polymerization initiator, and the like can be appropriately selected from those known in the art and used for the preparation of the polymeric dispersant (B).

The ratio (% by mole) of each monomer unit in the polymer dispersant (B) to the total monomer units can be used¹H-NMR analysis was carried out.

[ Properties of Polymer dispersant ]

The number average molecular weight of the polymer dispersant (B) is not particularly limited, but is preferably 100 ten thousand or more, more preferably 200 ten thousand or more, further preferably 300 ten thousand or more, and preferably 2500 ten thousand or less, more preferably 1500 ten thousand or less, further preferably 1000 ten thousand or less. Here, the number average molecular weight of the polymeric dispersant can be calculated by using gel permeation chromatography using water as an eluent and comparing with a calibration curve based on standard polyethylene glycol.

Specific examples of the polymer dispersant (B) are described below, but the polymer dispersant (B) used in the present invention is not limited thereto. (Note that, in the following examples, the numerical values shown in parentheses after the names of the monomers indicate the content (mol%) of the monomer units derived from the monomers in the polymer dispersants (B), and the "molar ratio" indicates the molar ratio of the monomer units in the polymer dispersants (B))

D-1) copolymer of sodium styrene sulfonate (50)/sodium acrylate (50) (molar ratio: 1/1, average degree of polymerization 2 ten thousand, number average molecular weight 300 ten thousand 2300)

D-2) copolymer of sodium styrene sulfonate (50)/sodium methacrylate (50) (molar ratio: 1/1, average degree of polymerization 3 ten thousand, number average molecular weight 472 ten thousand 8500)

D-3) copolymer of sodium styrene sulfonate (66.7)/potassium methacrylate (33.3) (molar ratio: 2/1, average degree of polymerization 5 ten thousand, number average molecular weight 871 ten thousand 0400)

D-4) copolymer of sodium styrene sulfonate (75)/disodium itaconate (25) (molar ratio: 3/1, average degree of polymerization 5 ten thousand, number average molecular weight 990 ten thousand 7800)

D-5a) copolymer of sodium styrene sulfonate (50)/disodium maleate (50) (molar ratio: 1/1, average degree of polymerization 2 ten thousand, number average molecular weight 366 ten thousand 2300)

D-5b) copolymer of sodium styrene sulfonate (50)/disodium maleate (50) (molar ratio: 1/1, average degree of polymerization 5 ten thousand, number average molecular weight 915 ten thousand 5700)

D-5c) copolymer of sodium styrene sulfonate (50)/disodium maleate (50) (molar ratio: 1/1, average degree of polymerization 9 ten thousand, number average molecular weight 1648 thousand 0300)

D-6) copolymer of sodium styrene sulfonate (75)/disodium maleate (25) (molar ratio: 3/1, average degree of polymerization 2 ten thousand, number average molecular weight 389 ten thousand 3000)

D-7) copolymer of ammonium styrene sulfonate (50)/diammonium maleate (50) (molar ratio: 1/1, average degree of polymerization 3 ten thousand, number average molecular weight 526 ten thousand 6700)

D-8) styrene sulfonic acid (50)/maleic acid (50) copolymer (molar ratio: 1/1, average degree of polymerization 2 ten thousand, number average molecular weight 322 ten thousand 2000)

D-9) copolymer of sodium styrenesulfonate (50)/disodium fumarate (50) (molar ratio: 1/1, average degree of polymerization 2 ten thousand, number average molecular weight 366 ten thousand 3300)

D-10) sodium vinylsulfonate (50)/sodium acrylate (50) copolymer (molar ratio: 1/1, average degree of polymerization 5 ten thousand, number average molecular weight 224 ten thousand 1400)

D-11) sodium allylsulfonate (50)/sodium acrylate (50) copolymer (molar ratio: 1/1, average degree of polymerization 2 ten thousand, number average molecular weight 238 ten thousand 1600)

D-12) acrylamide-sodium N-butanesulfonate (50)/sodium acrylate (50) (molar ratio: 1/1, average degree of polymerization 8 ten thousand, number average molecular weight 1205 ten thousand 1600)

D-13) copolymer of sodium styrene sulfonate (40)/disodium maleate (40)/acrylamide (20) (molar ratio: 2/2/1, average degree of polymerization 3 ten thousand, number average molecular weight 557 ten thousand 7300)

D-14) copolymer of sodium styrene sulfonate (40)/disodium maleate (40)/sodium monomethyl maleate (20) (molar ratio: 2/2/1, average degree of polymerization of 1.5 ten thousand, number average molecular weight 297 ten thousand 7600)

D-15) copolymer of sodium styrene sulfonate (50)/disodium maleate (33.3)/sodium acrylate (16.7) (molar ratio: 3/2/1, average degree of polymerization 2.5 ten thousand, number average molecular weight 497 ten thousand 7300)

The concentration of the polymer dispersant (B) in the CNT dispersion liquid of the present invention is preferably 0.0001% by mass or more, more preferably 0.01% by mass or more, particularly preferably 0.05% by mass or more, preferably 30% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less. By setting the concentration of the polymer dispersant (B) to 0.0001 mass% or more, the stability of the CNT dispersion and the adhesion of the conductive film formed from the CNT dispersion to the substrate can be improved, and by setting the concentration to 30 mass% or less, the conductivity of the conductive film formed from the CNT dispersion can be secured.

Further, the content of the polymer dispersant (B) in the CNT dispersion liquid of the present invention is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, preferably 1000 parts by mass or less, more preferably 700 parts by mass or less, and particularly preferably 400 parts by mass or less, per 100 parts by mass of the carbon nanotubes (a). By including the polymer dispersant (B) in the CNT dispersion liquid in an amount of 50 parts by mass or more per 100 parts by mass of the carbon nanotube (a), the stability of the CNT dispersion liquid and the adhesion of the conductive film formed from the CNT dispersion liquid to the substrate can be improved, and by including the polymer dispersant (B) in an amount of 1000 parts by mass or less, the conductivity of the conductive film formed from the CNT dispersion liquid can be secured.

In the CNT dispersion liquid of the present invention, there is no problem even when a dispersant other than the polymer dispersant (B) is used in combination, and the use of the dispersant in combination is not limited to improve the dispersibility. As further dispersants, it is possible to use: various ionic and nonionic surfactants, synthetic polymers other than the polymer dispersant (B), natural polymers, and the like.

< solvent (C) >

The solvent (C) may be aqueous or organic, but an aqueous solvent is preferably used (that is, it is preferable that the solvent (C) contains water). Here. The aqueous solvent is not particularly limited as long as it is a solvent in which CNTs can be dispersed, and water may be used alone or a mixed solvent of water and a solvent may be used. As the solvent to be mixed with water, there can be mentioned: ethers (dioxane, tetrahydrofuran, methyl cellosolve, etc.), ether alcohols (ethoxyethanol, methoxyethoxyethanol, etc.), esters (methyl acetate, ethyl acetate, etc.), ketones (cyclohexanone, methyl ethyl ketone, etc.), alcohols (ethanol, isopropanol, phenol, etc.), lower carboxylic acids (acetic acid, etc.), amines (triethylamine, trimethanolamine, etc.), nitrogen-containing polar solvents (N, N-dimethylformamide, nitromethane, N-methylpyrrolidone, acetonitrile, etc.), sulfur compounds (dimethyl sulfoxide, etc.), and the like. Among these, ethers, alcohols, and N, N-dimethylformamide are preferable as the solvent to be mixed with water, from the viewpoint of improving the stability of the CNT dispersion.

When the solvent (C) of the CNT dispersion contains water, the pH of the CNT dispersion is not particularly limited, but is preferably 0.1 or more, more preferably 0.2 or more, particularly preferably 0.5 or more, preferably 8 or less, more preferably less than 7 (i.e., acidic), further preferably 5 or less, and particularly preferably 2.5 or less. By setting the pH of the CNT dispersion to the above range, the stability of the CNT dispersion can be ensured.

In order to lower the pH of the CNT dispersion, an acidic substance may be added. As the acidic substance, for example, sulfuric acid, hydrochloric acid, nitric acid, citric acid, oxalic acid, tartaric acid, formic acid, phosphoric acid, and the like are preferably used, and hydrochloric acid and nitric acid are more preferably used.

< preparation of carbon nanotube Dispersion >

The CNT dispersion liquid of the present invention can be prepared by mixing CNT (a), a polymer dispersant (B) and a solvent (C) using, for example, a mixing and dispersing machine described in japanese patent application laid-open No. 2013-199419. Among them, the use of an ultrasonic homogenizer is preferred because it is simple. In the mixing, cnt (a) may be in a dry state or may include a solvent. The CNT dispersion may be in a liquid state or a semisolid state such as a paste or a gel, but is preferably in a liquid state.

(conductive film and conductive film)

The conductive film of the present invention is formed using the CNT dispersion of the present invention. Such a conductive film has excellent adhesion to a substrate. The conductive film of the present invention is excellent in handling properties, and therefore is suitably used for a conductive film obtained by forming the conductive film on a substrate.

< substrate >

The substrate is not particularly limited in shape, constituent material, and size (thickness, etc.) as long as the resulting conductive film can be supported by the carbon nanotube dispersion liquid applied thereon, and can be appropriately selected according to the intended use.

Examples of the shape of the substrate include: films, sheets, and the like.

Among the materials constituting the substrate, as inorganic materials, there can be mentioned: stainless steel, metals such as aluminum, iron, gold, and silver, and glass. The organic material may be a carbon material, a plastic substrate material, or the like, but a plastic substrate material is preferable from the viewpoint of improving adhesiveness to the conductive film, and stretch-following ability and flexibility of the conductive film. Further, as the plastic substrate material, a material having high heat resistance, excellent chemical resistance and gas barrier property, and low cost is preferable. In addition, the plastic substrate material may be a material having transparency without coloring. As such specific plastic substrate materials, for example: polyesters (polyethylene terephthalate (PET), polyethylene naphthalate (PEN), etc.), styrenes (syndiotactic polystyrene (SPS), etc.), polyphenylene sulfide (PPS), Polycarbonate (PC), polyarylate (PAr), Polysulfone (PSF), polyester sulfone (PES), Polyetherimide (PEI), transparent Polyimide (PI), cycloolefin copolymer (trade name "ARTON" (registered trademark), etc.), alicyclic polyolefin (trade name "ZEONOR" (registered trademark), etc.), polycarbonate, polyamide, polyurethane, polymethyl methacrylate, cellulose triacetate, etc. Among them, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and alicyclic polyolefin are particularly preferable from the viewpoint of chemical stability and cost.

When a plastic substrate material is used as the base material, the thickness of the base material is not particularly limited, and may be in various ranges from a medium thickness to a very thin thickness. The thickness of the substrate in this case is preferably 1 to 1000. mu.m, more preferably 5 to 500. mu.m, and particularly preferably 20 to 200. mu.m.

By using a transparent substrate as the substrate, a conductive film having excellent transparency and conductivity can be obtained. In the present invention, the "substrate having transparency" means a substrate having a light transmittance of 50% or more at a wavelength of 550 nm.

In the present invention, the light transmittance of the substrate at a wavelength of 550nm can be measured by the method for measuring "light transmittance of the conductive film at a wavelength of 550 nm" described in the examples of the present specification.

As the substrate, a substrate provided with an undercoat layer may be used.

The substrate may be subjected to surface hydrophilization treatment such as glow discharge, corona discharge treatment, or ozone treatment on the surface to be coated with the CNT dispersion to form a conductive film.

Further, the surface of the substrate opposite to the surface to be coated with the CNT dispersion may be subjected to hard coating treatment for imparting abrasion resistance, high surface hardness, solvent resistance, stain resistance, fingerprint resistance, and the like.

< formation of conductive film >

The conductive film can be formed, for example, by applying the CNT dispersion liquid of the present invention to the substrate (coating step) and then drying the CNT dispersion liquid on the substrate (drying step).

[ coating Process ]

The method for applying the CNT dispersion of the present invention to a substrate is not particularly limited, and a known application method, for example, the method described in japanese patent application laid-open No. 2013-199419, can be used. Further, the coating may be performed not only once but also a plurality of times as needed, or two different coating methods may be combined. Particularly preferred coating methods include: wire rod coating, gravure coating and spraying.

As described above, the CNT dispersion liquid of the present invention can realize a higher concentration than the conventional CNT dispersion liquid, and can increase the CNT coating amount per unit area of the substrate to a desired value with a smaller number of coating times.

The coating thickness (wet thickness) of the CNT dispersion on the substrate is not particularly limited as long as the conductivity of the obtained film can be secured, and is preferably 0.001 to 50 μm, more preferably 0.005 to 10 μm, and particularly preferably 0.01 to 3 μm.

The amount of CNT coating per unit area of the substrate when the CNT dispersion is coated on the substrate is preferably 0.001mg/m²～50g/m²More preferably 0.005mg/m²～10g/m²Particularly preferably 0.01mg/m²～3g/m²。

[ drying Process ]

After the CNT dispersion is applied to the substrate, the CNT dispersion on the substrate is dried by a method such as air drying, heating, or pressure reduction, to form a conductive film on the substrate. The drying temperature is not particularly limited as long as the solvent (C) can be removed by vaporization and the heat-resistant temperature of the base material is not higher than the heat-resistant temperature. For example, when the plastic substrate material is used as the base material, the drying temperature is preferably 0 to 250 ℃, more preferably 15 to 150 ℃, and particularly preferably 80 to 150 ℃.

< removal of dispersant or the like in conductive film >

In addition, since the conductive film of the present invention may contain a dispersant other than the polymer dispersant (B), an arbitrary binder material, or the like, it is also possible to remove these components in particular to improve the conductivity of the conductive film. As a method for removing the dispersant and the like, there is a method in which after a conductive film is formed on a substrate, the obtained conductive film is immersed in a cleaning solvent, or the cleaning solvent is sprayed onto the conductive film on the substrate. The solvent for washing is not particularly limited as long as it can sufficiently dissolve the dispersant to be removed and does not remove the cnts (a), and examples thereof include: water, alcohols, acetonitrile.

< Properties of conductive film >

The conductive film of the present invention has excellent adhesion to a substrate. The conductive film is formed using the CNT dispersion liquid of the present invention, and is excellent in mechanical properties such as film strength and scratch resistance, and as a result, the film itself is not easily broken but strongly stays on the substrate, and it is estimated that the conductive film exhibits excellent adhesiveness.

In addition, the conductive film of the present invention can exhibit excellent conductivity because cnts (a) in the conductive film are dispersed appropriately. The conductive film of the present invention has a surface resistivity of preferably 20 Ω/□ or less, more preferably 10 Ω/□ or less, and the lower limit is usually about 0.01 Ω/□, more preferably 0.1 Ω/□. The surface resistivity of the conductive film of the present invention can be measured by the method described in the examples of the present specification.

The conductive film of the present invention may be provided with transparency by appropriately adjusting the amount of cnt (a) contained therein, and for example, a transparent conductive film may be obtained by using the above-described transparent substrate as a substrate. The light transmittance of such a conductive film at a wavelength of 550nm is preferably 50% or more, more preferably 60% or more, further preferably 70% or more, further more preferably 80% or more, and particularly preferably 90% or more. The light transmittance of the conductive film of the present invention at a wavelength of 550nm can be measured by the method described in the examples of the present specification.

< use of conductive film >

The use of the conductive film of the present invention is not particularly limited, and for example, the conductive film can be used in the use described in japanese patent application laid-open No. 2013-199419.

The conductive film of the present invention is particularly suitable for use as a photoelectrode substrate and a counter electrode substrate of a dye-sensitized solar cell (DSC).