JP6197353B2 - Carbon nanotube dispersion - Google Patents

Description

  The present invention relates to a dispersion of carbon nanotubes and a composite material excellent in dispersibility.

Conventionally, many methods for obtaining a dispersion of carbon nanotubes having excellent dispersion stability using a dispersant have been studied. For example, a method using a naturally occurring detergent such as taurocholic acid, cyclodextrin, saponin as a dispersant (Patent Document 1), or a method using a synthetic surfactant such as sodium dodecyl sulfate in water as a dispersant (Patent Document 1) 2 example, paragraph 0004 of patent document 3) is known. However, in order to ensure dispersion stability, it may be necessary to use a large amount of surfactant, and depending on the use of the dispersion, the surfactant may have an adverse effect.
Further, it is known that carbon nanotubes are dispersed in an amide polar organic solvent by using a nonionic surfactant instead of an anionic surfactant such as sodium dodecyl sulfate (Patent Document 4).

JP-T-2004-534714 JP 2002-264097 A JP 2007-320828 A Japanese Patent Laid-Open No. 2005-077561

  An object of the present invention is to provide a carbon nanotube dispersion liquid that suppresses aggregation of carbon nanotubes in a solvent and exhibits high dispersion stability.

According to the present invention, a carbon nanotube having an average diameter (Av) and a diameter distribution (3σ) of 0.60> 3σ / Av> 0.20, an aromatic having 30 mol% or more of a structural unit derived from an aromatic vinyl compound. A carbon nanotube dispersion containing an aromatic vinyl compound polymer and a solvent is provided. The aromatic vinyl compound polymer is preferably a homopolymer of a styrene derivative or a copolymer of a styrene derivative and a methacrylic acid derivative. The solvent is preferably a nitrogen-containing polar solvent.
Moreover, according to this invention, the molded object manufactured using the said dispersion liquid is provided.

Hereinafter, the present invention will be specifically described based on embodiments.
As the carbon nanotube used in the present invention, a known single-walled or multi-walled carbon nanotube can be used. In the present invention, any carbon nanotube can be used as a nanocarbon material. Among them, a carbon nanotube satisfying an average diameter (Av) and a diameter distribution (3σ) of 0.60> 3σ / Av> 0.20. Is difficult to obtain dispersion stability in a dispersion medium due to the influence of its van der Waals force. However, when a surfactant represented by the above formula (1) is used, high dispersion stability can be obtained even in a small amount. Is obtained.
Particularly preferred carbon nanotubes in the present invention have an average diameter (Av) and a diameter distribution (3σ) satisfying 0.60> 3σ / Av> 0.20. Here, the average diameter (Av) and the diameter distribution (3σ) are obtained by multiplying the average value when the diameter of 100 carbon nanotubes is measured with a transmission electron microscope and the standard deviation (σ) by 3. . In addition, the standard deviation in this specification is a sample standard deviation.
A composition exhibiting excellent conductivity even when the amount of carbon nanotubes is small by using carbon nanotubes having an average diameter (Av) and a diameter distribution (3σ) satisfying 0.60> 3σ / Av> 0.20. Can be obtained. From the viewpoint of the characteristics of the obtained composition, 0.60> 3σ / Av> 0.25 is more preferable, and 0.60> 3σ / Av> 0.50 is more preferable.
3σ / Av represents the diameter distribution of the carbon nanotube, and the larger the value, the wider the diameter distribution. In the present invention, the diameter distribution is preferably a normal distribution. The diameter distribution here refers to the diameter of 100 randomly selected carbon nanotubes that can be observed using a transmission electron microscope, and the results are used to calculate the diameter on the horizontal axis and the frequency on the vertical axis. And plotting the obtained data and approximating with Gaussian. The value of 3σ / Av can also be increased by combining a plurality of types of carbon nanotubes obtained by different production methods, but in this case, it is difficult to obtain a normal distribution of diameters. That is, in the present invention, it is preferable to use a single carbon nanotube or a single carbon nanotube mixed with another carbon nanotube in an amount that does not affect the diameter distribution.
Carbon nanotubes satisfying 0.60> 3σ / Av> 0.20 can be used without particular limitation, but are described in Japanese Patent No. 4621896 and Japanese Patent No. 4811712. Carbon nanotubes obtained by the super growth method (hereinafter sometimes referred to as “SGCNT”) are preferred. SGCNT is a carbon nanotube having a peak of Radial Breathing Mode (RBM) in Raman spectroscopy. Note that there is no RBM in the Raman spectrum of multi-walled carbon nanotubes of three or more layers.

In the present invention, an aromatic vinyl compound polymer having a structural unit derived from an aromatic vinyl compound of 30 mol% or more functions as a dispersant. In order to function sufficiently as a dispersant, the lower limit of the structural unit derived from the aromatic vinyl compound in the aromatic vinyl compound polymer is 30 mol% or more, preferably 40 mol% or more, and the upper limit is preferably 100 mol%.
The weight average molecular weight of the aromatic vinyl compound polymer is usually 1,000 to 1,000,000, preferably 3,000 to 500,000, more preferably 4,000 to 100,000. If the weight average molecular weight is too small, sufficient dispersibility cannot be obtained. Conversely, if the weight average molecular weight is too large, it is difficult to obtain a good quality dispersion without dissolving in the dispersion medium.
As structural units derived from such aromatic vinyl compounds, styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene, monofluorostyrene, hydroxymethylstyrene, N, N-dimethylaminoethylstyrene, N, N-diethylaminoethylstyrene, N Styrene derivatives such as N, N-dipropylaminoethylstyrene and N, N-dioctylaminoethylstyrene; vinyl polyaromatic compounds such as vinylnaphthalene, vinylpyrene, vinylbenzopyrene, vinylanthracene, vinylindene and vinylfluorene; , From the viewpoint of use of, as the structural units derived from these aromatic vinyl compounds, styrene derivatives are preferred.
Examples of the aromatic vinyl compound polymer having a structural unit derived from such an aromatic vinyl compound include polystyrene; a block of a styrene derivative and an acrylic acid derivative such as acrylic acid, methacrylic acid, acrylic acid ester, and methacrylic acid ester. Examples thereof include block copolymers and random copolymers of styrene derivatives and conjugated dienes such as butadiene and isoprene, and hydrogenated products thereof. These can be manufactured according to the information. Further, these aromatic vinyl compound-based polymers can have any functional group depending on the use of the dispersion. From the viewpoint of dispersibility, among these aromatic vinyl compound-based polymers, homopolymers of styrene derivatives and copolymers of styrene derivatives and methacrylic acid derivatives are particularly preferable. It is preferable that it is 2 times or more, preferably 3 times or more with respect to the weight of the carbon nanotube. If the amount of the aromatic vinyl compound-based polymer is too large, it may be precipitated in the dispersion, whereas if it is too small, the dispersibility of the dispersion may not be sufficiently obtained. Further, when the polymer concentration is too high, there is a problem that the viscosity of the solution is increased and the dispersion treatment becomes an obstacle.

  The dispersion medium used in the present invention is not particularly limited as long as it is a nitrogen-containing polar solvent, but N-methylpyrrolidone, dimethylformamide or dimethylacetamide can be advantageously obtained as an effect as a dispersant for an aromatic vinyl compound polymer. Is preferred. The concentration of the aromatic vinyl compound polymer in the dispersion medium is preferably in the range of 1 mg / mL to 20 mg / mL.

  There is no particular limitation on the method for obtaining the carbon nanotube dispersion, and the carbon nanotube and the aromatic vinyl compound polymer may be added to a nitrogen-containing polar solvent as a dispersion medium, followed by a dispersion treatment according to a conventional method. There is no particular restriction on the order of the carbon nanotubes and the aromatic vinyl compound polymer added to the dispersion medium, either of which may be added first or simultaneously. Examples of the dispersion treatment include a method of directly stirring the dispersion using a stirrer, and a dispersion method capable of obtaining a cavitation effect. Dispersion that provides a cavitation effect is a dispersion method that uses shock waves generated by bursting of vacuum bubbles generated in water when high energy is applied to the liquid. By using the dispersion method, carbon nanotubes are obtained. It becomes possible to disperse in water without impairing the characteristics of the. Specific examples of the dispersion treatment that provides a cavitation effect include dispersion treatment using ultrasonic waves, dispersion treatment using a jet mill, and dispersion treatment using high shear stirring. Only one method may be employed for the distributed processing, or a plurality of distributed processing methods may be combined. A conventionally known apparatus may be used as the apparatus used for the distributed processing.

  Various additives can be blended in the dispersion of the present invention depending on the purpose of use. Additives include antioxidants, heat stabilizers, light stabilizers, UV absorbers, pigments, colorants, foaming agents, antistatic agents, flame retardants, lubricants, softeners, tackifiers, plasticizers, release agents Agents, deodorants, fragrances and the like.

  The dispersion of the present invention can be used for various applications such as the production of a coating film and the production of a plastic molded body. At this time, a polymer latex, a polymer solution, and various additives can be used in combination.

Production Example 1 (Synthesis of carbon nanotube)
SGCNTs were obtained by the super-growth method as described in Japanese Patent No. 4621896.
Specifically, carbon nanotubes were grown under the following conditions.
Carbon compound: ethylene; supply rate 50 sccm
Atmosphere (gas) (Pa): Helium, hydrogen mixed gas; supply rate 1000 sccm
Pressure 1 atmospheric pressure water vapor addition amount (ppm): 300 ppm
Reaction temperature (° C): 750 ° C
Reaction time (min): 10 minutes Metal catalyst (abundance): Iron thin film; thickness 1 nm
Substrate: Silicon wafer The obtained SGCNT has a BET specific surface area of 1,050 m ² / g and a radial breathing mode (100 to 300 cm ^{−1) in} a low-frequency region (100 to 300 cm ⁻¹⁾ , which is characteristic of a single-walled CNT. RBM) spectrum was observed. Moreover, as a result of measuring the diameter of 100 SGCNT-1 at random using a transmission electron microscope, average diameter (Av) is 3.3 nm, diameter distribution (3σ) is 1.9, (3σ / Av) Was 0.58.

<Example 1>
Polystyrene (styrene homopolymer; Wako Pure Chemical, Mw: 73000, Mw / Mn: 3.8) was dissolved in dimethylacetamide (DMAc) to a concentration of 10 mg / mL to obtain a polystyrene solution. 1 mg of SGCNT obtained in Production Example 1 and 5 mL of a sealed polystyrene solution were stirred in a sample bottle, and further using an ultrasonic irradiator (BRANSON, product name “Bransonic (registered trademark) 5510”). Ultrasonic irradiation was performed for 60 minutes. No visible particles were present in the solution after ultrasonic irradiation. The obtained solution was centrifuged (10000 × G, 1 hour) using a centrifuge (product name “CS-100GXII” manufactured by Hitachi Koki Co., Ltd.), and then a spectrophotometer (manufactured by JASCO Corporation, UK). The absorption spectrum was measured with the product name “V7200”). The absorbance at an optical path length of 1 mm and a wavelength of 1000 nm was 0.91.
<Example 2>
An SGCNT dispersion solution was prepared and evaluated in the same manner as in Example 1 except that the solvent was changed to dimethylformamide (DMF). As a result, a solution having no visible particles was obtained, and the absorbance of the absorption spectrum was 0.84.
<Example 3>
An SGCNT dispersion was prepared in the same procedure as in Example 1, except that DMAc was used as the solvent and polystyrene (styrene homopolymer; manufactured by Agilent Technologies, Mw: 70,000) was used as the polymer. As a result, a solution having no visible particles was obtained, and the absorbance of the absorption spectrum was 0.86.
<Example 4>
An SGCNT dispersion was prepared in the same procedure as in Example 3, except that polystyrene (styrene homopolymer; manufactured by Agilent Technologies, Mw: 5000) was used as the polymer. As a result, a solution having no visible particles was obtained, and the absorbance of the absorption spectrum was 0.86.
<Example 5>
An SGCNT dispersion was prepared in the same procedure as in Example 3, except that polystyrene (styrene homopolymer; manufactured by Agilent Technologies, Mw: 200000) was used as the polymer. As a result, a solution without visible particles was obtained, and the absorbance of the absorption spectrum was 0.83.
<Example 6>
Styrene-methyl methacrylate random copolymer (manufactured by Polymer Standard Service, Mw: 50700, styrene / methyl methacrylate = 80/20 (weight ratio), aromatic vinyl compound-derived structural unit 80 mol%) is used as the polymer. A SGCNT dispersion was prepared in the same procedure as in Example 3, except that As a result, a solution without visible particles was obtained, and the absorbance of the absorption spectrum was 0.89.
<Example 7>
Styrene-methyl methacrylate random copolymer (Polymer Standard Service, Mw: 87700, styrene / methyl methacrylate = 51/49 (weight ratio), aromatic vinyl compound-derived structural unit 50 mol%) is used as the polymer. A SGCNT dispersion was prepared in the same procedure as in Example 3, except that As a result, a solution without visible particles was obtained, and the absorbance of the absorption spectrum was 0.82.
<Example 8>
Styrene-methyl methacrylate block copolymer (manufactured by Polymer Standard Service, Mw: 50000, polystyrene block Mw: 22000, polymethyl methacrylate block: Mw: 28000, aromatic vinyl compound-derived structural unit 43 mol) %) Was used in the same procedure as in Example 3 to prepare an SGCNT dispersion. As a result, a solution having no visible particles was obtained, and the absorbance of the absorption spectrum was 0.84.
<Example 9>
Styrene-methyl methacrylate block copolymer (manufactured by Polymer Standard Service, Mw: 184000, polystyrene block Mw: 89000, polymethyl methacrylate block Mw: 95000, aromatic vinyl compound-derived structural unit 47 mol%) SGCNT dispersion was prepared in the same procedure as in Example 3 except that was used. As a result, a solution having no visible particles was obtained, and the absorbance of the absorption spectrum was 0.87.

<Comparative Example 1>
An SGCNT dispersion was prepared in the same procedure as in Example 3, except that polystyrene (styrene homopolymer; manufactured by Agilent Technologies, Mw: 3000) was used as the polymer. Numerous aggregates were observed after ultrasonic irradiation, and the absorbance of the absorption spectrum after removing the aggregates by centrifugation was 0.12.
<Comparative example 2>
An SGCNT dispersion was prepared in the same procedure as in Example 3 except that polystyrene (styrene homopolymer; manufactured by Agilent Technologies, Mw: 1000000) was used as the polymer. Numerous aggregates were observed after ultrasonic irradiation, and the absorbance of the absorption spectrum after removing the aggregates by centrifugation was 0.09.
<Comparative Example 3>
SGCNT dispersion liquid in the same procedure as in Example 7 except that a styrene-methyl methacrylate random copolymer (Polymer Standard Service, Mw: 103000, aromatic vinyl compound-derived structural unit 19 mol%) was used as the polymer. Was prepared. Numerous aggregates were observed after ultrasonic irradiation, and the absorbance of the absorption spectrum after removing the aggregates by centrifugation was 0.10.
<Comparative example 4>
HiPco (manufactured by Nanointegris, SuperPure grade, BET specific surface area 700 m ² / g, average diameter (Av) 1.1 nm, diameter distribution (3σ) 0.2, (3σ / Av) 0.18) A CNT dispersion was prepared in the same procedure as in Example 1 except that was used. Numerous aggregates were observed after ultrasonic irradiation, and the absorbance of the absorption spectrum after removing the aggregates by centrifugation was 0.18.
<Comparative Example 5>
Multi-walled carbon nanotubes (manufactured by Nanostructured & Amorphous Materials Inc., Lot. 1232, BET specific surface area 57 m ² / g, average diameter (Av) 51.1 nm, diameter distribution (3σ) 9.8, (3σ A CNT dispersion was prepared in the same procedure as in Example 1, except that / Av) was 0.19). Numerous aggregates were observed after ultrasonic irradiation, and the absorbance of the absorption spectrum after removing the aggregates by centrifugation was 0.17.

<Example 10>
150 μl of the CNT dispersion prepared in Example 1 was dropped on a 1 cm × 4 cm glass plate and heated on a hot plate for 8 hours to form a film. It measured using the surface resistance value (The Mitsubishi Chemical Analytech Co., Ltd. make, product name "Loresta (trademark) GP MCP-T600") of the produced coating film. Moreover, the dispersion state of CNT in the coating film was observed and evaluated using an optical microscope (product name “KH-1300” manufactured by Hilox). The surface resistance value was 742Ω / □, and no agglomerates that were visible in the microscopic image were observed, and a uniform coating film was obtained.
<Example 11>
Film formation and evaluation were performed in the same manner as in Example 10 except that the dispersion liquid prepared in Example 2 was used as the dispersion liquid for film formation. As a result, the surface resistance value was 783 Ω / □, and no agglomerates that were visible in the microscopic image were observed, and a uniform coating film was obtained.
<Example 12>
Film formation and evaluation were performed in the same manner as in Example 10 except that the dispersion liquid prepared in Example 3 was used as the dispersion liquid for film formation. As a result, the surface resistance value was 819 Ω / □, and no agglomerates that were visible in the microscopic image were found, and a uniform coating film was obtained.
<Example 13>
Film formation and evaluation were performed in the same manner as in Example 10 except that the dispersion liquid prepared in Example 7 was used as the dispersion liquid for film formation. As a result, the surface resistance value was 942Ω / □, and no agglomerates that were visible in the microscopic image were observed, and a uniform coating film was obtained.
<Example 14>
Film formation and evaluation were performed in the same manner as in Example 10 except that the dispersion liquid prepared in Example 9 was used as the dispersion liquid for film formation. As a result, the surface resistance value was 863 Ω / □, and no agglomerates that were visible in the microscopic image were observed, and a uniform coating film was obtained.

<Comparative Example 6>
Film formation and evaluation were performed in the same manner as in Example 10 except that the dispersion prepared by the method of Comparative Example 1 was used as the dispersion for film formation. As a result, the surface resistance value was 43423 Ω / □, and many black spots that were considered to be aggregates of CNTs were observed in the microscopic image.
<Comparative Example 7>
Film formation and evaluation were performed in the same manner as in Example 10 except that the dispersion liquid prepared by the method of Comparative Example 2 was used as the dispersion liquid for film formation. As a result, the surface resistance value was 18463 Ω / □, and many black spots that were considered to be aggregates of CNTs were observed in the microscopic image.
<Comparative Example 8>
Film formation and evaluation were performed in the same manner as in Example 10 except that the dispersion liquid prepared by the method of Comparative Example 5 was used as the dispersion liquid for film formation. As a result, the surface resistance value was 27645 Ω / □, and many black spots that were considered to be aggregates of CNTs were observed in the microscopic image .

  From these results, in order to efficiently obtain a uniform carbon nanotube solution using a polymer containing an aromatic vinyl compound component, a solvent containing nitrogen is used as a solvent, and the aromatic vinyl compound content of the polymer used is 30 mol. It can be seen that it is necessary to satisfy all of the three conditions that the carbon nanotube has a specific diameter distribution exceeding 50%. A dispersion satisfying these conditions is useful for producing a low-resistance coating film.

Claims (4)

Carbon nanotubes having an average diameter (Av) and a diameter distribution (3σ) of 0.60> 3σ / Av>0.20;
Styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2 -Methylstyrene, monochlorostyrene, dichlorostyrene, monofluorostyrene, hydroxymethylstyrene, N, N-dimethylaminoethylstyrene, N, N-diethylaminoethylstyrene, N, N-dipropylaminoethylstyrene, N, N-dioctyl 30 mol% or more of structural units derived from at least one aromatic vinyl compound selected from the group consisting of aminoethylstyrene, vinylnaphthalene, vinylpyrene, vinylbenzopyrene, vinylanthracene, vinylindene and vinylfluorene, and weight average And an aromatic vinyl compound polymer molecular weight is 4,000～700,000,
A nitrogen-containing polar solvent;
A carbon nanotube dispersion containing The aromatic vinyl compound polymer is styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t- Butylstyrene, 5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene, monofluorostyrene, hydroxymethylstyrene, N, N-dimethylaminoethylstyrene, N, N-diethylaminoethylstyrene, N, N-di 2. A homopolymer of at least one styrene derivative selected from the group consisting of propylaminoethylstyrene and N, N-dioctylaminoethylstyrene, or a copolymer of the styrene derivative and a methacrylic acid derivative. Carbon nanotube dispersion liquid. The manufacturing method of a molded object including the process of manufacturing a molded object using the carbon nanotube dispersion liquid of Claim 1 or 2 . The manufacturing method of a coating film including the process of forming a coating film using the carbon nanotube dispersion liquid of Claim 1 or 2.