JP2019212496A - Carbon nanotube water-based dispersion - Google Patents

Abstract

To provide a carbon nanotube water-based dispersion good in dispersibility of a carbon nanotube, and good in wettability to a PET film, and a manufacturing method therefor.SOLUTION: There is provided a carbon nanotube water-based dispersion containing components A to C, in which the component A is a carbon nanotube, the component B is a polymer dispersant, the component C is a binder resin containing a constitutional unit derived from (meth)acrylic acid, and the polymer dispersion is a polymer compound in which pH of 1 mass% solution thereof at 25°C is 5 to 8.SELECTED DRAWING: None

Description

  The present disclosure relates to a carbon nanotube aqueous dispersion and a method for producing the same.

  A carbon nanotube is a nanocarbon material having a cylindrical shape formed by winding a single graphite surface. Single-walled carbon nanotubes are wound in one layer, and multi-walled carbon nanotubes are coaxially wound in multiple layers. That's it. Carbon nanotubes themselves have excellent intrinsic conductivity and are expected to be used as conductive materials.

  Since the carbon nanotube has a high aspect ratio and can form a conductive path with a small amount, the carbon nanotube can be a conductive material excellent in light transmittance and drop-off resistance as compared with conventional conductive fine particles such as carbon black. For example, it is known to use a carbon nanotube as a transparent conductive thin film for optics.

  In order to obtain a conductive film excellent in light transmittance using carbon nanotubes, a thick bundle consisting of several tens of carbon nanotubes and strong aggregation are solved, and carbon nanotubes are highly dispersed to reduce carbon content. It is required to efficiently form a conductive path with the number of nanotubes. As a means for obtaining such a conductive film, for example, a method of applying a dispersion obtained by highly dispersing carbon nanotubes in a solvent to a substrate is known. In order to highly disperse carbon nanotubes in a solvent, there is a technique of dispersing using a dispersant. Above all, in order to disperse carbon nanotubes to a higher degree, a method of dispersing in an aqueous solvent using a dispersant having both a hydrophilic group having affinity for water and a hydrophobic group having high affinity for carbon nanotubes. Is known (see, for example, Patent Document 1).

WO2014-002885

However, the technique described in Patent Document 1 has a problem that even if it is applied to a PET film, the wettability of the surface is poor and it cannot be applied well. In such a case, there is a method of treating the surface of the PET film before coating, but this is disadvantageous in terms of process and cost.
It is known to add an organic solvent to improve the wettability of the PET film surface. However, if it is added in a large amount until the effect is exerted, it is disadvantageous in terms of cost, and the flash point is lowered, making it difficult to handle. There is concern. Furthermore, there is a concern that the dispersibility of the carbon nanotubes is deteriorated.

  Therefore, in one aspect, the present disclosure provides a carbon nanotube aqueous dispersion having good dispersibility of carbon nanotubes and improved wettability to a resin surface such as a PET film surface and a method for producing the same.

  In one aspect, the present disclosure includes components A to C, the component A is a carbon nanotube, the component B is a polymer dispersant, and the component C is a binder including a structural unit derived from (meth) acrylic acid. The resin and the polymer dispersing agent relate to a carbon nanotube aqueous dispersion, which is a polymer compound having a pH of 5 to 8 at 25 ° C. in a 1 mass% aqueous solution thereof.

In another aspect, the present disclosure is a method for producing a carbon nanotube aqueous dispersion,
A step of mixing a carbon nanotube, a polymer dispersant, a binder resin containing a structural unit derived from (meth) acrylic acid, and an aqueous medium, and dispersing the carbon nanotube in the aqueous solvent;
The polymer dispersant relates to a method for producing a carbon nanotube aqueous dispersion, which is a polymer compound having a pH of 5 or more and 8 or less at 25 ° C. in an aqueous solution having a concentration of 1% by mass.

  According to the present disclosure, in one or a plurality of embodiments, it is possible to provide a carbon nanotube aqueous dispersion and a method for producing the same, in which the dispersibility of the carbon nanotubes is good and the wettability with respect to the resin surface such as the PET film surface is improved. .

  As a result of intensive studies, the present inventors have found that an aqueous dispersion of carbon nanotubes is a polymer dispersant having a pH of 5 to 8 at 25 ° C. in a 1% by mass aqueous solution, and a structure derived from (meth) acrylic acid. By including a binder resin containing a unit, the wettability with respect to a resin surface such as a PET film surface is improved while maintaining the dispersibility of carbon nanotubes (hereinafter sometimes referred to as “CNT”). It has been found that an aqueous dispersion of carbon nanotubes capable of directly forming a coating film on the surface can be obtained, and the present disclosure has been completed.

The details of the mechanism of the effect of the present disclosure are not clear, but are presumed as follows.
When the carbon nanotube aqueous dispersion contains a polymer dispersant (component B) having a pH of 5 to 8 at 25 ° C. in a 1 mass% aqueous solution, the dispersibility of CNT (component A) is good, but PET Even if it is applied to a resin surface such as a film surface, it does not repel and becomes a coating film. However, the carbon nanotube aqueous dispersion further contains a structural unit derived from (meth) acrylic acid, and a binder resin (component C) that assists the dispersibility of the CNT, and the dispersibility of the CNT and the resin surface such as the PET film surface. A specific monoalcohol (component D) that can reduce both the coating properties and the surface tension of the dispersion without affecting the dispersibility of the CNTs if the amount is a predetermined amount because of its low affinity with CNTs. ) In combination, it is considered that the dispersibility of CNTs and the coating properties on the resin surface such as the surface of the PET film can be better balanced. However, the present disclosure is not construed as being limited to these mechanisms.

That is, in one aspect, the present disclosure relates to a CNT dispersion that is a carbon nanotube aqueous dispersion (hereinafter, also referred to as “CNT dispersion of the present disclosure”) including the following components A to C.
Component A: Carbon nanotube component B: Polymer dispersant having a pH of 5 to 8 at 25 ° C. in a 1% by mass aqueous solution Component C: Binder resin containing a structural unit derived from (meth) acrylic acid

[CNT dispersion]
According to the present disclosure, it is possible to provide a CNT dispersion liquid that has good CNT dispersibility and improved wettability with respect to a resin surface such as a PET film surface. Since the CNT dispersion liquid of the present disclosure has good wettability to a resin surface such as a PET film surface, a good coating film can be directly formed on a resin surface such as a PET film surface with one liquid. Therefore, the CNT dispersion liquid of the present disclosure is a CNT dispersion liquid suitable for coating on the resin surface.

[CNT (component A)]
In the present disclosure, the CNT means a whole including a plurality of CNTs. The form of CNT is not particularly limited. For example, a plurality of CNTs may be independent from each other, a form such that a plurality of CNTs are bundled or entangled, or these forms are mixed. Form may be sufficient. The CNTs may be CNTs with various numbers of layers or diameters. The CNTs may contain impurities derived from processes in the production of CNTs (eg, catalysts and amorphous carbon).

  In one or a plurality of embodiments, the CNT has a shape in which one surface of graphite is wound into a cylindrical shape, and a single layer CNT is wound in one layer, and two layers are wound in two layers. A CNT wound in three or more layers is also referred to as a multilayer CNT. In the CNT dispersion and the coating film obtained by applying the dispersion, single-layer, double-layer, and multilayer CNTs and mixtures thereof can be used depending on the required application characteristics. In particular, it is preferable to use single-walled CNTs in order to obtain a highly light-transmitting conductive coating film.

  The length of the CNT is measured by a scanning electron microscope (SEM) or an atomic force microscope (AFM). In the present invention, the length is not particularly limited, and from the viewpoint of high conductivity, 0.5 μm or more is preferable, more preferably 1 μm or more, and 30 μm or less is preferable from the viewpoint of high dispersibility.

  The content of impurities in the CNT is measured by a method such as thermogravimetric analysis, but it is better to be as small as possible in the present invention. The content of impurities in the CNT is preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less, and even more preferably 10% by mass or less from the viewpoint of increasing the effective content of the CNT. Preferably, substantially 0% by weight is even more preferred.

The CNT content in the CNT dispersion of the present disclosure can be higher than that in the conventional CNT dispersion. Specifically, 0.04% by mass or more is preferable, 0.05% by mass or more is more preferable, 0.06% by mass or more is more preferable, and from the viewpoint of making the dispersion easy to handle, 0.5 % By mass or less is preferable, 0.4% by mass or less is more preferable, and 0.3% by mass or less is still more preferable.

[Polymer dispersant (component B)]
The dispersant contained in the CNT dispersion is a polymer dispersant (component B) from the viewpoint of suppressing foaming, and preferably has a neutral pH from the viewpoint of suppressing corrosion of the apparatus. In the present application, the pH of the polymer dispersant being neutral means that the 1% by mass aqueous solution of the polymer dispersant (component B) is 5 or more and 8 or less at 25 ° C.

The polymer dispersant (component B) is preferably a polymer compound having a sugar skeleton, more preferably a neutralized carboxymethyl cellulose, and ammonium is preferable as a neutralizing ion.

  From the viewpoint of improving dispersibility, the viscosity at 25 ° C. of the 1% by mass aqueous solution of Component B is preferably 1 mPa · s or more, more preferably 3 mPa · s or more, further preferably 5 mPa · s or more, and the same viewpoint. 500 mPa · s or less, preferably 400 mPa · s or less, and more preferably 300 mPa · s or less.

  The content of Component B in the CNT dispersion liquid of the present disclosure is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and further 70 parts by mass or more with respect to 100 parts by mass of CNTs from the viewpoint of improving dispersibility. Preferably, from the viewpoint of cost reduction of the dispersion, 500 parts by mass or less is preferable, 400 parts by mass or less is more preferable, and 300 parts by mass or less is still more preferable.

[Binder resin (component C)]
The CNT dispersion liquid of the present disclosure includes a binder resin containing a structural unit derived from (meth) acrylic acid from the viewpoint of improving wettability to a resin surface such as a PET film surface and improving dispersibility of CNTs. Component C may be used alone or in combination of two or more.

  The structural unit derived from (meth) acrylic acid in all the structural units constituting Component C is preferably 90 mol% or more, more preferably 95 mol% or more, still more preferably 97 mol% or more, from the viewpoint of improving the dispersibility of CNTs. And from a viewpoint of wettability improvement, 100 mol% or less is preferable.

Component C further includes a structural unit derived from a hydrophobic monomer having a hydrophobic group having high affinity with the resin surface such as the PET film surface from the viewpoint of improving the wettability with respect to the resin surface such as the PET film surface. And preferred. In the case where Component C is a copolymer of (meth) acrylic acid and a hydrophobic monomer, it can be produced by polymerizing (meth) acrylic acid and a hydrophobic monomer.

In the present disclosure, the hydrophobic monomer refers to a monomer having a solubility in water at 25 ° C. of less than 10% by mass. Dissolution means that the solute is mixed with a uniform solvent and exhibits a transparent state. Examples of the hydrophobic monomer include methoxydipropylene glycol acrylate (MPG2A), phenoxydiethylene glycol acrylate, methyl acrylate, ethyl acrylate, butyl acrylate, and phenyl acrylate.

  The structural unit derived from the hydrophobic monomer in all the structural units constituting Component C is preferably 10 mol% or less, more preferably 5 mol% or less, still more preferably 3 mol% or less, from the viewpoint of improving the dispersibility of CNTs, and From the viewpoint of improving wettability, 0 mol% or more is preferable.

  Component C may further include other structural units in one or more embodiments. In one or a plurality of embodiments, the total amount of the structural unit derived from (meth) acrylic acid and the structural unit derived from the hydrophobic monomer in all the structural units constituting Component C is preferably 80 mol% or more, and 90 mol% or more. More preferably, substantially 100 mol% is still more preferable.

  The number average molecular weight of component C is preferably 5,000 or more, more preferably 6,000 or more, and 7,000 or more from the viewpoint of improving wettability with respect to a resin surface such as a PET film surface and improving dispersibility of CNTs. Further, from the same viewpoint, 30,000 or less is preferable, 25,000 or less is more preferable, and 20,000 or less is more preferable. More specifically, the number average molecular weight of Component C is preferably 5,000 or more and 30,000 or less, more preferably 6,000 or more and 25,000, and still more preferably 7,000 or more and 20,000 or less. The number average molecular weight of component C can be measured using a gel permeation chromatography (hereinafter also referred to as “GPC”) method, and specifically can be calculated by the method described in the examples.

  In the present disclosure, the component C preferably has a low degree of neutralization from the viewpoint of improving the dispersibility of the CNT, and the neutralization degree of the component C is a neutralizable functional group (for example, a carboxy group) contained in the component C. ) 100 mol%, preferably 25 mol% or less, more preferably less than 25 mol%, more preferably 10 mol% or less from the viewpoint of improving dispersibility, and substantially not neutralized. Further preferred. Specifically, the degree of neutralization of Component C when not substantially neutralized is preferably 1 mol% or less, and more preferably 0 mol%. The degree of neutralization can be calculated by, for example, pH measurement.

  Component C can be produced by a known polymerization method. For the polymerization, a known polymerization initiator, chain transfer agent, or the like can be used. Examples of the polymerization initiator include 2,2-azobis (isobutyronitrile) (hydrophobic), 2,2-azobis (2,4-dimethylvaleronitrile) (hydrophobic), 2,2-azobis [N And azo-initiated polymerization agents such as-(2-carboxyethyl) -2-methylpropionamidine] hydrate (water-soluble) and 2,2-azobis [2-methylpropionamidine] dihydrochloride (water-soluble). . Examples of the chain transfer agent include 3-mercaptopropionic acid (hydrophilic), mercaptopropanediol (water-soluble), 1-octanethiol (hydrophobic), and the like.

  The content of Component C in the CNT dispersion liquid of the present disclosure is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and 0.03% by mass from the viewpoint of improving adhesion to a PET film. % Or less is more preferable, and from the same viewpoint, 0.5% by mass or less is preferable, 0.4% by mass or less is more preferable, and 0.3% by mass or less is more preferable.

  The content of Component C in the CNT dispersion liquid of the present disclosure is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and further preferably 50 parts by mass or more with respect to 100 parts by mass of CNTs from the viewpoint of improving dispersibility. And from a viewpoint of cost reduction of a dispersion liquid, 300 mass parts or less are preferable, 250 mass parts or less are more preferable, and 200 mass parts or less are still more preferable.

ただし、前記一般式（１）中、Ｒ¹、Ｒ²は同一、もしくは異なって、水素原子又はメチル基（−ＣＨ₃）を示す。 [Monoalcohol having 1 to 4 carbon atoms (component D)]
The CNT dispersion liquid of the present disclosure preferably contains a monoalcohol having 1 to 4 carbon atoms from the viewpoint of improving wettability to PET. As the component C, for example, methyl alcohol (MeOH), ethyl alcohol (EtOH), isopropanol (IPA), i-butyl alcohol (iBuOH), sec-butyl alcohol (sBuOH), and tert-butyl alcohol (tBuOH) are used. Although at least 1 sort (s) chosen from a group is mentioned, from a viewpoint of safety | security and a foaming suppression viewpoint, ethyl alcohol (EtOH), isopropanol (IPA), i-butyl alcohol (iBuOH), sec-butyl alcohol (sBuOH) ) And at least one selected from the group consisting of tert-butyl alcohol (tBuOH), and from the viewpoint of improving wettability to PET, among methanol and monoalcohols represented by the following general formula (1) At least one of Properly, ethyl alcohol, isopropanol, and t- butyl least one selected from alcohol is more preferable.

However, the general formula ^{(1), R 1, R} 2 are identical or different, represent a hydrogen atom or a methyl group (-CH _3).

The content of component D in the CNT dispersion of the present disclosure is preferably 5% by mass or more, more preferably 6% by mass or more, still more preferably 7% by mass or more, from the viewpoint of improving wettability to PET, and From the viewpoint of ease of handling in consideration of the flash point and cost reduction, it is preferably 20% by mass or less, more preferably 19% by mass or less, and still more preferably 18% by mass or less.

  The content of component D in the CNT dispersion liquid of the present disclosure is preferably 1 part by mass or more and more preferably 1.5 parts by mass or more from the viewpoint of improving wettability to PET when the aqueous solvent is 100 parts by mass. 2 parts by mass or more is more preferable. Moreover, 25 mass parts or less are preferable from a viewpoint of the ease of handling which considered flash point, and cost, 24 mass parts or less are more preferable, and 23 mass parts or less are still more preferable.

[Aqueous solvent]
The CNT dispersion of the present disclosure is an aqueous dispersion containing an aqueous solvent. The aqueous medium is preferably water, and examples thereof include distilled water, ion exchange water, and ultrapure water. The aqueous medium is preferably composed only of water, but the aqueous solvent contains other solvents other than the water-soluble organic solvent other than the component D in addition to water as long as the dispersibility of CNTs is not impaired. May be. When the aqueous solvent is a mixed solvent of water and the water-soluble organic solvent, the water-soluble organic solvent may be added (blended) separately from water, or may be added (blended) simultaneously with water. Good. The content of water in the mixed solvent is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and 95 parts by mass when the mixed solvent is 100 parts by mass from the viewpoint of ease of handling in consideration of the flash point and cost reduction. The above is more preferable.

  The content of the aqueous medium in the CNT dispersion of the present disclosure may be an amount such that the viscosity at 25 ° C. of the CNT dispersion is a value in the following range from the viewpoint of ease of coating, For example, 80 mass% or more is preferable, 82 mass% or more is more preferable, and from the viewpoint of improving wettability with respect to a PET film, 93 mass% or less is preferable, and 91 mass% or less is more preferable.

  The viscosity of the CNT dispersion of the present disclosure is preferably 1 mPa · s or higher, more preferably 10 mPa · s or higher, more preferably 20 mPa · s or higher, at 25 ° C., from the viewpoint of ease of coating. In view of the above, 2000 mPa · s or less is preferred, 1500 mPa · s or less is more preferred, and 1000 mPa · s or less is even more preferred. More specifically, the viscosity of the CNT dispersion of the present disclosure is preferably 1 mPa · s or more and 2000 mPa · s or less, more preferably 10 mPa · s or more and 1500 mPa · s or less, and further preferably 20 mPa · s or more and 1000 mPa · s or less. .

The viscosity of the CNT dispersion can be measured, for example, as follows.
[Viscosity of CNT dispersion at shear rate of 10 s ^-1 ]
Brookfield viscometer cone plate type (cone radius 12 mm, cone angle 3 °), viscosity is read after rotating at a shear rate of 10 s ^-1 for 60 seconds. The measurement temperature is 25 ° C.

[Method for producing CNT dispersion]
The method for producing a CNT dispersion of the present disclosure includes the following first step and second step.
1st process: A carbon nanotube, a polymer dispersing agent, and an aqueous medium are mixed, The said carbon nanotube is disperse | distributed to the said aqueous solvent, and the liquid mixture for CNT dispersion liquid preparation is obtained.
Second step: The CNT dispersion liquid mixture and a monoalcohol having 1 to 4 carbon atoms are mixed.
However, in either one or both of the first step and the second step, a binder resin containing a structural unit derived from (meth) acrylic acid is mixed with other components.

  The CNT dispersion of the present disclosure includes, for example, CNT (component A), a polymer dispersant (component B), a binder resin (component C), a specific monoalcohol (component D), and an aqueous solvent by a known method. Can be manufactured. Therefore, in one aspect of the present disclosure, CNT (component A), a polymer dispersant (component B), and an aqueous solvent are mixed, and the CNT is dispersed in the aqueous solvent. CNT dispersion manufacturing method (hereinafter referred to as “this”), which includes a first step to be obtained and a second step in which a binder resin (component C) and a monoalcohol (component D) are added to and mixed with a mixture for preparing a CNT dispersion. Also referred to as “disclosed dispersion manufacturing method”. Moreover, the dispersion manufacturing method of this indication WHEREIN: In another aspect, CNT (component A), a polymer dispersing agent (component B), binder resin (component C), and an aqueous solvent are mixed, CNT is made in an aqueous solvent. A first step of obtaining a mixed liquid for preparing a CNT dispersion by dispersing and a second step of adding and mixing monoalcohol (component D) to the mixed liquid for preparing a CNT dispersion are included. From the viewpoint of improving the dispersibility of CNTs, the first step is preferably the first step. According to the method for producing a CNT dispersion of the present disclosure, a CNT dispersion having excellent dispersibility and wettability with respect to PET can be produced. As the components A to D and the aqueous solvent used in the method for producing the CNT dispersion of the present disclosure, the same ones as those of the CNT dispersion of the present disclosure described above can be used.

  In the first step and the second step, a mixed liquid for preparing a CNT dispersion and a CNT dispersion can be produced using a general mixing and dispersing machine for producing a paint, respectively. Examples of the mixing and dispersing machine include at least one selected from an ultrasonic homogenizer, a vibration mill, a jet mill, a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, a high pressure homogenizer, an ultrasonic device, an attritor, a resolver, a paint shaker, and the like. Is mentioned. In the first step, it is preferable to disperse CNTs using ultrasonic waves from the viewpoint of improving dispersibility. In the second step, a general mixing method using stirring may be used. The CNT used for the preparation of the CNT dispersion may be in a dry state or a CNT composition containing a solvent. In the second step, the preferable blending amount of each component can be the same as the preferable content of the CNT dispersion liquid of the present disclosure described above.

  In addition, when manufacturing the CNT dispersion liquid which does not contain the component D, the said process 2 can be skipped.

[Coating on resin film]
The CNT dispersion of the present invention can be used for coating on a resin film. Although it does not specifically limit as a resin film, PET resin film is mentioned. As for the coating means, brush coating, spray spraying, dipping and the like can be mentioned, but there is no particular limitation.

  Hereinafter, the present disclosure will be described in more detail by way of examples. However, these examples are illustrative, and the present disclosure is not limited to these examples.

1. Method for Measuring Number Average Molecular Weight Using gel permeation chromatography (hereinafter also referred to as “GPC”), the number average molecular weight of Component C and its comparative object was measured.
That is, a sample (component C and its comparative object) was diluted with N, N-dimethylformamide to prepare a solution having a solid content concentration of 0.3% by mass as a sample solution, and 100 μL thereof was used for measurement. . As an eluent, a solution obtained by dissolving phosphoric acid and lithium bromide in N, N-dimethylformamide so as to have concentrations of 60 mmol / L and 50 mmol / L, respectively, GPC [apparatus: “HLC-8120GPC” manufactured by Tosoh Corporation, Detector: differential refractometer (attached to the device), column: “TSK-GEL α-M” x 2 manufactured by Tosoh Corporation, column temperature: 40 ° C., eluent flow rate: 1 mL / min].
As a standard substance, polystyrene (manufactured by Tosoh Corporation: molecular weights 5.26 × 10 ² , 1.02 × 10 ⁵ , 8.42 × 10 ⁶ ; Nishio Kogyo Co., Ltd .: molecular weight 4.0 × 10 ³ , 3. 0 × 10 ⁴ , 9.0 × 10 ⁵ ) were used.

2. Preparation of binder resin The following components were used for the preparation of the aqueous solution of the binder resin.
Acrylic acid (Reagent manufactured by Wako Pure Chemical Industries, Ltd.)
<Hydrophobic monomer>
MPG2A: Methoxydipropylene glycol acrylate (Kyoei Chemical Co., Ltd. “Light acrylate DPM-A”, solubility in water at 25 ° C .: 2% by mass)
<Polymerization initiator>
VA-057: 2,2-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate (reagent “VA-057” manufactured by Wako Pure Chemical Industries, Ltd.)
<Chain transfer agent>
MPA: 3-mercaptopropionic acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.)

[Synthesis of binder resin]
[Binder resin A]
A 1 L 4-neck separable flask was charged with 15.0 g of distilled water in advance, and two dropping funnels, a reflux condenser, a thermometer, and a stirring device were attached. After nitrogen substitution, the temperature was raised to 80 ° C. while stirring at 150 rpm, and while maintaining the temperature, a mixed solution of 80% by mass acrylic acid aqueous solution: 60.6 g and MPG2A (hydrophobic monomer): 1.5 g, and VA −057 (polymerization initiator): 0.56 g and MPA (chain transfer agent): 0.36 g and distilled water: 47.9 g of mixed solutions were separately added dropwise over 60 minutes. After completion of dropping, the temperature was kept at 80 ° C. for 60 minutes, and then cooled. The solid content concentration of the aqueous solution of the obtained binder resin A (molar ratio (acrylic acid / MPG2A) = (98.9 / 1.1)) is 42.6% by mass, and the polystyrene-equivalent number average molecular weight by GPC is 19350. Met.

[Binder resin B]
A 1 L 4-neck separable flask was charged with 15.0 g of distilled water in advance, and two dropping funnels, a reflux condenser, a thermometer, and a stirring device were attached. After purging with nitrogen, the temperature was raised to 80 ° C. while stirring at 150 rpm, and while maintaining the temperature, a mixed solution of 80 mass% acrylic acid aqueous solution: 58.1 g and MPG2A (hydrophobic monomer): 3.5 g, and VA −057 (polymerization initiator): 1.37 g, MPA (chain transfer agent): 1.62 g, and distilled water: 48.4 g of mixed solutions were separately added dropwise over 60 minutes. After completion of dropping, the temperature was kept at 80 ° C. for 60 minutes, and then cooled. The solid content concentration of the aqueous solution of the obtained binder resin B (molar ratio (acrylic acid / MPG2A) = (97.4 / 2.6)) is 43.5% by mass, and the number average molecular weight in terms of polystyrene by GPC is 6700. Met.

[Binder resin C]
A 1 L 4-neck separable flask was charged with 15.0 g of distilled water in advance, and two dropping funnels, a reflux condenser, a thermometer, and a stirring device were attached. After carrying out nitrogen substitution, it heated up to 80 degreeC, stirring at 150 rpm, 80 mass% acrylic acid aqueous solution: 62.5g, VA-057 (polymerization initiator): 0.86g, and MPA (while maintaining temperature) Chain transfer agent): A mixed solution of 0.37 g and distilled water: 47.5 g was separately added dropwise over 60 minutes. After completion of dropping, the temperature was kept at 80 ° C. for 60 minutes, and then cooled. The solid content concentration of the aqueous solution of the obtained binder resin C (polyacrylic acid) was 42.4% by mass, and the polystyrene equivalent number average molecular weight by GPC was 24700.

3. Preparation of mixed liquids 1 to 4 for preparing CNT dispersion liquid Carboxymethylcellulose ammonium as a polymer dispersing agent (Daicel Co., Ltd., DN-10L, pH of 1% by weight aqueous solution at 25 ° C. is 7, 25% of 1% by weight aqueous solution. Viscosity is 10 to 50 mPa · s (catalog value)), CNT, binder resin A aqueous solution (mixed liquid 4 for preparing CNT dispersion only) and aqueous medium (distilled water) are mixed so as to have the concentrations shown in Table 1. Then, liquid mixtures 1 to 4 for preparing the CNT dispersion were prepared.

  Specifically, an aqueous solution of the polymer dispersant, an aqueous solution of the binder resin A (only used for preparing the mixed solution 4 for preparing the CNT dispersion), and distilled water are added to a 60 mL screw tube so that the total amount becomes 40 g. Weighed and then weighed 0.08 g of CNTs and mixed them. The obtained mixture was stirred with a 2 cm long stirrer chip at 300 rpm for 1 hour, and then dispersed with an ultrasonic homogenizer (300 μA) for 13 minutes while cooling with ice, to obtain CNT dispersion liquid mixtures 1-4. Got. US-300 manufactured by Nippon Seiki Seisakusho was used as the ultrasonic homogenizer. As the CNT, “TUBALL” (single-walled carbon nanotubes having a purity of 75%, 1 to 2 layers, 5 μm or more in length) manufactured by OCSiAl was used.

4). Preparation of CNT dispersion liquid Aqueous medium in aqueous solutions of CNT dispersion mixture liquids 1 to 4 obtained above, monoalcohol, and optionally binder resins A to C obtained by [synthesis of binder resin] 1% by weight binder resin aqueous solution obtained by adding (distilled water) and, if necessary, an aqueous medium (distilled water), CNT, polymer dispersant, binder resin, monoalcohol each having a predetermined concentration The CNT dispersions of Examples 1 to 12 and Comparative Examples 1 to 3 were obtained. The contents of CNT, polymer dispersant, binder resin, and monoalcohol in each CNT dispersion with 100% by mass of the CNT dispersion are as shown in Table 2.

5. Evaluation
[Distributed state]
Evaluation of the dispersion state of CNTs in the CNT dispersion liquid mixture and the CNT dispersion liquid was judged visually.
(Visually)
It was confirmed whether CNT aggregates were observed on the wall surface of the screw tube. The results are shown in Tables 1 and 2.
<Evaluation criteria>
A: The number of aggregates adsorbed on the glass wall surface is ² or less per 1 cm ² .
B: The number of aggregates adsorbed on the glass wall surface is within 3 to 5 grains per 1 cm ² .
C: The number of aggregates adsorbed on the glass wall surface is 6 or more per 1 cm ² .
D: Not dispersed at all When the evaluation criteria are A and B, it is judged that the dispersibility of CNT is good.

[Wettability to PET film]
As a PET film, Lumirror T60 (100 μm) manufactured by Toray Industries, Inc. was used. The prepared CNT dispersions of Examples 1 to 12 were mixed with spiral bar coater No. The coating surface was observed after drying for 1 minute with a blow dryer at 100 ° C. The evaluation criteria are shown below. The evaluation results are shown in Table 2. In Table 2, when evaluation criteria are A, B, and C, it is judged that the wettability with respect to PET film is favorable.
<Evaluation criteria>
A: No repelling is observed B: Repelling is observed at one or two places.
C: 3 to 10 repels can be seen.
D: Clearly more than 10 repels are seen.
In addition, in the CNT dispersion liquids of Comparative Examples 1 to 3, since CNTs were aggregated, coating was impossible before the evaluation of wettability.

  From the results shown in Table 2, it can be seen that the CNT dispersions of Examples 1 to 12 have good CNT dispersibility and wettability to the PET film. That is, since the CNT dispersion liquids of Examples 1 to 12 have good wettability to the PET film surface, it is possible to form a good coating film directly on the PET film surface with one liquid even without an undercoat layer. It is.

  Since the CNT dispersion liquid of the present disclosure contains a neutral polymer dispersant and a specific binder resin, the dispersibility of the CNT is good and the wettability to the PET film is excellent. The CNT dispersion of the present disclosure can contribute to lowering the resistance of the conductive transparent film formed using the CNT dispersion.

Claims (11)

  The component A includes carbon nanotubes, the component B is a polymer dispersant, the component C is a binder resin including a structural unit derived from (meth) acrylic acid, and the polymer dispersant is An aqueous dispersion of carbon nanotubes, which is a polymer compound having a pH of 5 to 8 at 25 ° C. in a 1% by mass aqueous solution thereof. The carbon nanotube aqueous dispersion further contains a monoalcohol (component D) having 1 to 4 carbon atoms,
The carbon nanotube aqueous dispersion according to claim 1, wherein the content of the component D is 5% by mass or more and 20% by mass or less.   The carbon nanotube aqueous dispersion according to claim 1 or 2, wherein the component A is a single-walled carbon nanotube.   The carbon nanotube aqueous dispersion according to any one of claims 1 to 3, wherein the component C includes a structural unit derived from the (meth) acrylic acid and a structural unit derived from a hydrophobic monomer.   The carbon nanotube aqueous dispersion according to any one of claims 1 to 4, wherein the component C has a number average molecular weight of 5,000 or more and 30,000 or less.   The carbon nanotube aqueous dispersion according to any one of claims 1 to 5, wherein the component B has a sugar skeleton. The carbon nanotube aqueous dispersion according to any one of claims 2 to 6, wherein component D is at least one monoalcohol of methanol and a monoalcohol represented by the following general formula (1).

However, in said general formula (1), R < ¹ >, R < ² > is the same or different and shows a hydrogen atom or a methyl group.   The carbon nanotube aqueous dispersion according to any one of claims 2 to 7, wherein D is at least one selected from ethyl alcohol, isopropanol, and t-butyl alcohol.   The carbon nanotube aqueous dispersion according to any one of claims 1 to 8, which is used for coating on a resin film. A method for producing a carbon nanotube aqueous dispersion,
A step of mixing a carbon nanotube, a polymer dispersant, a binder resin containing a structural unit derived from (meth) acrylic acid, and an aqueous medium, and dispersing the carbon nanotube in the aqueous solvent;
The said polymer dispersing agent is a manufacturing method of the carbon nanotube aqueous dispersion which is a high molecular compound whose pH in 25 degreeC of the aqueous solution whose density | concentration is 1 mass% is 5-8. The carbon nanotube aqueous dispersion contains a monoalcohol having 1 to 4 carbon atoms,
The manufacturing method includes:
A first step of mixing a carbon nanotube, a polymer dispersant, and an aqueous medium, and dispersing the carbon nanotube in the aqueous solvent to obtain a mixed liquid for preparing a CNT dispersion;
A second step of mixing the mixed liquid for preparing the CNT dispersion and a monoalcohol having 1 to 4 carbon atoms,
11. The carbon nanotube aqueous dispersion according to claim 10, wherein a binder resin containing a structural unit derived from (meth) acrylic acid is mixed with another component in one or both of the first step and the second step. Manufacturing method.