JPWO2019188977A1 - Free-standing film, laminate, and method for manufacturing free-standing film - Google Patents

Abstract

An object of the present invention is to provide a self-supporting film composed of a plurality of fibrous carbon nanostructures having excellent light transmittance. The self-supporting film of the present invention is a self-supporting film composed of a plurality of fibrous carbon nanostructures, and the ratio of the G-band peak intensity to the D-band peak intensity (G / D ratio) in the Raman spectrum is 2 or more. The light transmittance at a wavelength of 550 nm is 60% or more, and the plurality of fibrous carbon nanostructures contain single-walled carbon nanotubes.

Description

The present invention relates to a self-supporting film, a laminate, and a method for producing a self-supporting film, and particularly includes a self-supporting film composed of a fibrous carbon nanostructure and a method for producing the same, and a self-supporting film composed of a fibrous carbon nanostructure. It relates to a laminate.

In recent years, fibrous carbon nanostructures such as carbon nanotubes (hereinafter, may be referred to as “CNT”) have been attracting attention as materials having excellent conductivity, thermal conductivity, and mechanical properties.

However, since fibrous carbon nanostructures such as CNTs are fine structures having a diameter of nanometers, they are poor in handleability and workability by themselves. Therefore, in order to secure handleability and processability and use it for various purposes, it has been conventionally practiced to form a carbon film by assembling a plurality of fibrous carbon nanostructures in a film shape (for example, a patent). Reference 1).

According to Patent Document 1, carbon obtained by forming a carbon film using a single-layer fibrous carbon nanostructure having a BET specific surface area of 500 m ^{2 / g or more and a multi-layer fibrous carbon nanostructure.} The independence and conductivity of the film can be enhanced.

Japanese Unexamined Patent Publication No. 2016-190772

Here, the carbon film is required to improve the light transmission while sufficiently ensuring its independence. In order to increase the light transmittance of the carbon film, for example, a method of reducing the thickness of the carbon film can be considered. However, in the above-mentioned conventional carbon film, if the thickness of the carbon film is reduced in order to enhance the light transmission, the independence of the carbon film may be impaired and it may be difficult to use the carbon film as an independent film.

Therefore, an object of the present invention is to provide a self-supporting film made of a plurality of fibrous carbon nanostructures having excellent light transmittance, a laminate having the self-supporting film, and a method for producing the self-supporting film. To do.

The present inventor has made diligent studies to achieve the above object. Then, the present inventor has found that a self-supporting film having excellent light transmittance can be obtained by adopting a predetermined procedure using a fibrous carbon nanostructure having a predetermined property, and the present invention has been developed. Completed.

That is, the present invention aims to solve the above problems advantageously, and the self-supporting film of the present invention is a self-supporting film composed of a plurality of fibrous carbon nanostructures, and D in the Raman spectrum. The ratio of G band peak intensity to band peak intensity (G / D ratio) is 2 or more, the light transmittance at a wavelength of 550 nm is 60% or more, and the plurality of fibrous carbon nanostructures are simply. It is characterized by containing layered carbon nanotubes. The self-supporting film described above has excellent light transmission.
In the present invention, the "self-supporting film" refers to a film that can maintain its film shape by itself without being damaged even in the absence of a support.
Further, in the present invention, the "ratio of G band peak intensity to D band peak intensity in Raman spectrum (G / D ratio)" of the self-supporting film and the fibrous carbon nanostructure is the method described in the examples of the present specification. Can be measured using.
Then, in the present invention, the "light transmittance of the free-standing film at a wavelength of 550 nm" can be measured by using the method described in the examples of the present specification.

Here, the self-supporting film of the present invention preferably has a thickness of 10 nm or more and 110 nm or less. When the thickness is within the above-mentioned range, the film strength of the free-standing film can be sufficiently ensured, and the light transmittance of the free-standing film can be further improved.
In the present invention, the "thickness" of the free-standing film can be measured by using the method described in the examples of the present specification.

The self-supporting film of the present invention preferably has a surface resistance value of 600 Ω / □ or less. A self-supporting film having a surface resistance value equal to or less than the above-mentioned value is excellent in conductivity.
In the present invention, the "surface resistance value" of the self-supporting film conforms to JIS K7194, and can be measured, for example, by using the method described in the examples of the present specification.
In addition, the free-standing film of the present invention preferably has a G-band peak intensity ratio (G / D ratio) of 10 or more to the D-band peak intensity in the Raman spectrum. A self-supporting film having a G / D ratio equal to or higher than the above-mentioned value has further excellent film strength.

Further, the present invention aims to solve the above problems advantageously, and the laminate of the present invention includes any of the above-mentioned free-standing films and a support in contact with the free-standing films. If the self-supporting film is treated as a laminate with the support, it is possible to prevent the self-supporting film from being damaged during storage, transportation, or the like.

Here, in the laminated body of the present invention, it is preferable that the surface roughness Ra of the surface of the support in contact with the free-standing film is 2.3 μm or less. If a support having a surface roughness Ra of 2.3 μm or less on the surface in contact with the free-standing film is used, the free-standing film can be easily peeled off from the support.
In the present invention, the "surface roughness Ra" of the support refers to the arithmetic mean roughness according to JIS B0601: 1994, and can be measured by using the method described in the examples of the present specification, for example. it can.

Further, the present invention aims to advantageously solve the above problems, and the method for producing a self-supporting film of the present invention is any of the above-mentioned methods for producing a self-supporting film, and is a single-walled carbon nanotube. A fibrous carbon nanostructure containing a plurality of fibrous carbon nanostructures containing, and having a G-band peak intensity ratio (G / D ratio) of 2 or more to the D-band peak intensity in the Raman spectrum, and a solvent. A step of supplying the dispersion liquid onto the support and a step of forming a laminate having a free-standing film on the support by removing the solvent from the fibrous carbon nanostructure dispersion liquid on the support. It is characterized by including a step of peeling the self-supporting film from the support by contacting the laminated body with a stripping solution having an SP value of 10 (MPa) ^{1/2 or more.} Through the above-mentioned steps, a self-supporting film having excellent light transmission can be efficiently produced.
The "SP value" in the present invention means the solubility parameter (SP value) of water or an organic solvent, and is a value represented by the square root of the molecular aggregation energy. The SP value is described in "Polymer HandBook (Second Edition) Chapter IV Solubility Parameter Values", and the value is used as the SP value in the present invention. (Note that the SP value refers to the value at 25 ° C.) In addition, for those for which no data is described, the calculation was performed by the method described in "RF Fedors, Polymer Engineering Science, 14, p147 (1967)". Let the value be the SP value in the present invention.

According to the present invention, it is possible to provide a self-supporting film made of a plurality of fibrous carbon nanostructures having excellent light transmittance, a laminate having the self-supporting film, and a method for producing the self-supporting film. it can.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the self-supporting film of the present invention is a self-supporting film composed of an aggregate of a plurality of fibrous carbon nanostructures. The method for producing an independent film of the present invention is a method for producing an independent film by assembling a plurality of fibrous carbon nanostructures into a film, and is used for producing the independent film of the present invention. The laminate of the present invention is provided with the self-supporting film of the present invention on a support, and can be obtained as a production intermediate when the self-supporting film of the present invention is manufactured by the method for producing the self-supporting film of the present invention. it can.

(Self-supporting membrane)
The self-supporting film of the present invention is a carbon film obtained by assembling and forming a film of a plurality of fibrous carbon nanostructures. The self-supporting membrane of the present invention may contain, for example, components (dispersant, etc.) other than the fibrous carbon nanostructures that are inevitably mixed in the manufacturing process. However, the ratio of the fibrous carbon nanostructures in the free-standing film is preferably 95% by mass or more, more preferably 98% by mass or more, further preferably 99% by mass or more, and 99% by mass. It is particularly preferably 5.5% by mass or more, and most preferably 100% by mass (that is, the free-standing film is composed of only fibrous carbon nanostructures).

<Characteristics>
<< G / D ratio >>
Here, the self-supporting film of the present invention needs to have a G / D ratio of 2 or more, and preferably 10 or more. If the G / D ratio is less than 2, the independence required for an independent film cannot be ensured. The reason for this is not clear, but when the G / D ratio is less than 2, the density of the self-supporting film decreases due to the increase in the proportion of the bent structure in the fibrous carbon nanostructures constituting the self-supporting film. It is presumed that this is because the film strength decreases.
The upper limit of the G / D ratio of the free-standing film is not particularly limited, but is usually 200 or less.

<< Light transmittance at wavelength 550 nm >>
Further, the self-supporting film of the present invention needs to have a light transmittance of 60% or more at a wavelength of 550 nm, preferably 85% or more, and more preferably 90% or more. A free-standing film having a light transmittance of less than 60% at a wavelength of 550 nm is inferior in light transmittance.

<< Surface resistance value >>
The self-supporting film of the present invention preferably has a surface resistance value of 600 Ω / □ or less. A self-supporting film having a surface resistance value of 600 Ω / □ or less is excellent in conductivity. The lower limit of the surface resistance value of the free-standing film is not particularly limited, but is usually 0.1 Ω / □ or more.

<< Thickness >>
Here, the self-supporting film of the present invention preferably has a thickness of 10 nm or more, more preferably 20 nm or more, preferably 110 nm or less, and more preferably 100 nm or less. When the thickness is 10 nm or more, the film strength of the free-standing film can be sufficiently secured, and when the thickness is 110 nm or less, the light transmittance of the free-standing film can be further improved.

<Fibrous carbon nanostructures>
As the plurality of fibrous carbon nanostructures constituting the self-supporting film of the present invention, it is necessary to use fibrous carbon nanostructures containing single-walled CNTs. If the plurality of fibrous carbon nanostructures constituting the self-supporting film do not contain single-walled CNTs, the light transmittance of the self-supporting film is lowered.
Here, the fibrous carbon nanostructure containing the single-walled CNT may be composed of only the single-walled CNT, or may be a mixture of the single-walled CNT and the fibrous carbon nanostructure other than the single-walled CNT. There may be. Examples of fibrous carbon nanostructures other than single-walled CNTs include multi-walled CNTs, vapor-grown carbon fibers, carbon fibers obtained by carbonizing organic fibers, and cut products thereof. These may be used alone or in combination of two or more.
The ratio of the single-walled CNTs in the fibrous carbon nanostructures is preferably 60% or more, more preferably 80% or more, further preferably 90% or more, and 100%. Most preferably, the fibrous carbon nanostructures consist only of single-walled CNTs.
The "ratio of single-walled CNTs in the fibrous carbon nanostructures" is to count the number of single-walled CNTs in 100 fibrous carbon nanostructures randomly selected using a transmission electron microscope. You can ask for it.

Further, as a fibrous carbon nanostructure containing a single-walled CNT, the ratio (3σ / Av) of the value (3σ) obtained by multiplying the standard deviation (σ) of the diameter by 3 with respect to the average diameter (Av) is 0.20. It is preferable to use a fibrous carbon nanostructure having an ultra-less than 0.60, more preferably to use a fibrous carbon nanostructure having a 3σ / Av of more than 0.25, and a fiber having a 3σ / Av of 0.50 or more. It is more preferred to use shaped carbon nanostructures. When the 3σ / Av of the fibrous carbon nanostructure is within the above-mentioned range, the film strength of the self-supporting film can be further increased and the conductivity can be improved.
The "average diameter of the fibrous carbon nanostructures (Av)" and the "standard deviation of the diameters of the fibrous carbon nanostructures (σ: sample standard deviation)" were randomly selected using a transmission electron microscope, respectively. The diameter (outer diameter) of 100 fibrous carbon nanostructures selected in 1 can be measured and obtained. The average diameter (Av) and standard deviation (σ) of the fibrous carbon nanostructures may be adjusted by changing the manufacturing method and manufacturing conditions of the fibrous carbon nanostructures, or may be obtained by different manufacturing methods. It may be adjusted by combining a plurality of types of the obtained fibrous carbon nanostructures.

The average diameter (Av) of the fibrous carbon nanostructure containing the single-walled CNT is preferably 0.5 nm or more, more preferably 1 nm or more, preferably 15 nm or less, and 10 nm or less. Is more preferable. When the average diameter (Av) of the fibrous carbon nanostructures is 0.5 nm or more, aggregation of the fibrous carbon nanostructures is suppressed to prevent a decrease in light transmission of the free-standing film due to the formation of aggregates. Can be done. On the other hand, when the average diameter (Av) of the fibrous carbon nanostructure is 15 nm or less, the film strength of the free-standing film can be further improved. In addition, if the average diameter (Av) of the fibrous carbon nanostructures is within the above range, the conductivity of the free-standing film can be enhanced.

Further, the BET specific surface area of the fibrous carbon nanostructure containing the single-walled CNT ^{is preferably 400 m 2} / g or more, more preferably 700 m ² / g or more, and 2500 m ² / g or less. It is preferably 1200 m ² / g or less, and more preferably 1200 m 2 / g or less. When the BET specific surface area of the fibrous carbon nanostructure is 400 m ² / g or more, the film strength of the free-standing film can be further improved. On the other hand, when the BET specific surface area of the fibrous carbon nanostructures is 2500 m ² / g or less, the aggregation of the fibrous carbon nanostructures is suppressed and the light transmittance of the free-standing film is prevented from being lowered due to the formation of aggregates. be able to. In addition, if the BET specific surface area of the fibrous carbon nanostructure is within the above range, the conductivity of the free-standing film can be enhanced.
In the present invention, the "BET specific surface area" refers to the nitrogen adsorption specific surface area measured by using the BET method.

As the fibrous carbon nanostructure containing the single-walled CNT, a commercially available product may be used. For example, the raw material compound and the carrier gas are supplied on a base material having a catalyst layer for CNT production on the surface. Therefore, when CNTs are synthesized by the chemical vapor phase growth method (CVD method), the presence of a small amount of oxidizing agent (catalyst activator) in the system dramatically improves the catalytic activity of the catalyst layer. The fibrous carbon nanostructure containing CNT may be efficiently produced according to the method (super growth method; see International Publication No. 2006/011655). In the following, the carbon nanotubes obtained by the super growth method may be referred to as "SGCNT".
Here, the fibrous carbon nanostructure containing SGCNT produced by the super growth method may be composed of only SGCNT, or in addition to SGCNT, for example, other carbon such as a non-cylindrical carbon nanostructure. Nanostructures may be included.

(Manufacturing method of self-supporting membrane)
The self-supporting film of the present invention described above can be produced by the method for producing a self-supporting film of the present invention. The method for producing a self-supporting film of the present invention is a plurality of fibrous fibers containing single-walled carbon nanotubes and having a ratio (G / D ratio) of G-band peak intensity to D-band peak intensity in the Raman spectrum of 2 or more. A step of supplying a fibrous carbon nanostructure dispersion containing a carbon nanostructure and a solvent onto a support (dispersion liquid supply step), and a step of removing the solvent from the fibrous carbon nanostructure dispersion on the support. By doing so, a step of forming a laminate having a self-supporting film on the support (laminate formation step) and a step of ^{bringing the laminate into contact with a stripping solution having an SP value of 10 (MPa) 1/2} or more can be used. At least a step of peeling the self-supporting film from the support (self-supporting film peeling step) is included. According to the production method of the present invention, a self-supporting film having excellent light transmission can be efficiently produced.

<< Dispersion liquid supply process >>
In the dispersion liquid supply step, the fibrous carbon nanostructure dispersion liquid in which the fibrous carbon nanostructures having a G / D ratio of 2 or more and containing single-walled CNTs are dispersed in a solvent (hereinafter, “dispersion”). (Sometimes abbreviated as "liquid") is supplied onto the support.

[Fibrous carbon nanostructure dispersion]
The dispersion contains the fibrous carbon nanostructures and the solvent, and optionally contains the fibrous carbon nanostructures and components other than the solvent (other components).

[Fibrous carbon nanostructures]
The fibrous carbon nanostructures contained in the dispersion are the fibrous carbon nanostructures constituting the self-supporting film of the present invention described above.
Here, the fibrous carbon nanostructure used for preparing the dispersion liquid needs to have a G / D ratio of 2 or more, and preferably 10 or more. The upper limit of the G / D ratio of the fibrous carbon nanostructure used for preparing the dispersion is not particularly limited, but is usually 1000 or less.
Further, the properties of the fibrous carbon nanostructures contained in the dispersion (excluding the above G / D ratio) usually match the properties of the fibrous carbon nanostructures described above in the section of "self-supporting film".
The concentration of the fibrous carbon nanostructures in the dispersion is not particularly limited as long as the fibrous carbon nanostructures can be dispersed in the solvent.

[solvent]
The solvent (dispersion medium of the fibrous carbon nanostructure) contained in the dispersion is not particularly limited, and is, for example, water, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-. Alcohols such as butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, amyl alcohol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, diethyl ether, dioxane, tetrahydrofuran and the like. Examples thereof include ethers, amide-based polar organic solvents such as N, N-dimethylformamide and N-methylpyrrolidone, and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene and paradichlorobenzene. Only one type of these may be used alone, or two or more types may be used in combination.

[Other ingredients]
The other components optionally contained in the dispersion are not particularly limited as long as they are known components that can be contained in the dispersion of the fibrous carbon nanostructure or the carbon film. For example, the dispersion liquid preferably contains a dispersant as another component.
The dispersant is not particularly limited as long as it can disperse the fibrous carbon nanostructures and can be dissolved in a solvent for dispersing the fibrous carbon nanostructures, and is not particularly limited. Alternatively, a natural polymer can be used.

Here, as the surfactant, any of an anionic surfactant, a cationic surfactant, and a nonionic surfactant can be used. Specific examples of the surfactant include sodium dodecylsulfonate, sodium deoxycholate, sodium cholic acid, sodium dodecylbenzenesulfonate and the like.
Examples of the synthetic polymer include polyether diol, polyester diol, polycarbonate diol, polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, acetal group-modified polyvinyl alcohol, butyral group-modified polyvinyl alcohol, and silanol group-modified. Polyvinyl alcohol, ethylene-vinyl alcohol copolymer, ethylene-vinyl alcohol-vinyl acetate copolymer resin, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, acrylic resin, epoxy resin, modified epoxy resin, phenoxy resin, modified phenoxy Examples thereof include resins, phenoxy ether resins, phenoxy ester resins, fluororesins, melamine resins, alkyd resins, phenol resins, polyacrylamides, polyacrylic acids, polystyrene sulfonic acids, polyethylene glycols, and polyvinylpyrrolidone.
Further, as natural polymers, for example, polysaccharides such as starch, pullulan, dextran, dextrin, guar gum, xanthan gum, amylose, amylopectin, alginic acid, arabic gum, carrageenan, chondroitin sulfate, hyaluronic acid, curdlan, chitin, chitosan, etc. Examples include cellulose and its salts or derivatives.
These dispersants can be used alone or in admixture of two or more.

And, among these dispersants, a surfactant is preferable. Further, as the surfactant, it is preferable to use a surfactant having a molecular weight of 400 or less, more preferably to use a surfactant having a molecular weight of 350 or less, and further to use a surfactant having a molecular weight of 300 or less. preferable. It is presumed that the surfactant having a molecular weight of 400 or less has the property of dispersing the fibrous carbon nanostructures in the solvent, but does not inhibit the network formation between the fibrous carbon nanostructures after the solvent is removed. However, by using a surfactant having a molecular weight of 400 or less, the self-supporting film can be satisfactorily peeled off from the support in the self-supporting film peeling step described later. Here, the lower limit of the molecular weight of the surfactant is not particularly limited, but is, for example, 50 or more. Examples of the surfactant having a molecular weight of 400 or less include sodium dodecylsulfonate (molecular weight: 288.38) and sodium dodecylbenzenesulfonate (molecular weight: 348.48). These can be used alone or in admixture of two or more.

Further, as the surfactant, it is preferable to use a surfactant having a linear alkyl chain having 6 or more and 20 or less carbon atoms. By using a surfactant having a linear alkyl chain having 6 to 20 carbon atoms, the self-supporting film can be satisfactorily peeled off from the support in the self-supporting film peeling step described later.

Among the surfactants, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate are preferable, and sodium dodecyl sulfonate is particularly preferable, from the viewpoint of satisfactorily peeling the self-supporting film from the support in the self-supporting film peeling step described later.

[Preparation method of dispersion]
Here, the method for preparing a dispersion liquid containing a plurality of fibrous carbon nanostructures, a solvent, and optionally other components such as a dispersant is as long as the fibrous carbon nanostructures can be dispersed in the solvent. There is no particular limitation. For example, the dispersion liquid includes a step of subjecting a composition containing a plurality of fibrous carbon nanostructures, a solvent, and optionally other components such as a dispersant to a dispersion treatment (dispersion treatment step), and the dispersion treatment. A step of allowing the subsequent composition to stand or centrifuge to precipitate a part of the plurality of fibrous carbon nanostructures (separation step), and a step of precipitating the supernatant from the standing or centrifuging composition as a liquid. It can be produced through a step of precipitating the state carbon nanostructure dispersion liquid (separation step). If the dispersion liquid is prepared through the above-mentioned dispersion treatment step, separation step, and preparative step, the light transmittance of the free-standing film obtained by using the dispersion liquid can be further improved.

-Dispersion processing process-
In the dispersion treatment step, a composition containing a plurality of fibrous carbon nanostructures, a solvent, and optionally other components such as a dispersant is subjected to a dispersion treatment. Here, the dispersion treatment method used in the dispersion treatment step is not particularly limited, and a known dispersion treatment method used for preparing the fibrous carbon nanostructure dispersion liquid can be used. Above all, as the dispersion treatment applied to the composition, a dispersion treatment capable of obtaining a cavitation effect or a crushing effect is preferable. By using a dispersion treatment that can obtain a cavitation effect or a crushing effect, the fibrous carbon nanostructures can be dispersed well, so that the film strength of the obtained free-standing film can be further increased.
Here, specific examples of the dispersion treatment for obtaining the cavitation effect and the dispersion treatment for obtaining the crushing effect are not particularly limited, and examples thereof include those described in JP-A-2016-183082.

The concentration of the fibrous carbon nanostructure containing the single-walled CNT in the composition to be subjected to the dispersion treatment is preferably 0.005% by mass or more, more preferably 0.01% by mass or more. It is preferably 5% by mass or less, and more preferably 3% by mass or less. When the concentration of the fibrous carbon nanostructures is 0.005% by mass or more, the concentration of the fibrous carbon nanostructures in the obtained dispersion is suppressed from decreasing, and a self-supporting film is efficiently produced. be able to. Further, when the concentration of the fibrous carbon nanostructures is 5% by mass or less, the aggregation of the fibrous carbon nanostructures can be suppressed, and the decrease in the light transmittance of the free-standing film due to the formation of the agglomerates can be prevented. ..
Further, the concentration of the dispersant in the composition to be subjected to the dispersion treatment is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and preferably 10% by mass or less. More preferably, it is 5% by mass or less. When the concentration of the dispersant is 0.1% by mass or more and 10% by mass or less, the fibrous carbon nanostructures having excellent dispersibility are appropriately left in the obtained supernatant (dispersion liquid), and the light transmittance is excellent. The self-supporting film can be efficiently produced.

-Separation process-
In the separation step, a part of the plurality of fibrous carbon nanostructures is precipitated by allowing the composition after the dispersion treatment described above to stand or centrifuge. Then, in the separation step, the fibrous carbon nanostructures having high cohesiveness are precipitated, and the fibrous carbon nanostructures having excellent dispersibility remain in the supernatant liquid.

The conditions under which the composition after the dispersion treatment is allowed to stand are not particularly limited as long as the precipitation and the supernatant are well separated. For example, the standing time is 1 hour or more from the viewpoint of efficiently producing a self-supporting film having excellent light transmittance by appropriately leaving fibrous carbon nanostructures having excellent dispersibility in the obtained supernatant liquid. It is preferably present, and more preferably 2 hours or more. The upper limit of the standing time is not particularly limited.

Further, the centrifugation of the composition after the dispersion treatment is not particularly limited, and can be performed using a known centrifuge.
Above all, from the viewpoint of efficiently producing a self-supporting film having excellent light transmittance by appropriately leaving fibrous carbon nanostructures having excellent dispersibility in the obtained supernatant, the composition after the dispersion treatment is centrifuged. The centrifugal rotation speed is preferably 10 rpm or more, more preferably 20 rpm or more, preferably 15,000 rpm or less, and more preferably 10,000 rpm or less.
Further, from the viewpoint of efficiently producing a self-supporting film having excellent light transmission by appropriately leaving the fibrous carbon nanostructures having excellent dispersibility in the obtained supernatant, the fibrous carbon nanostructures dispersion is centrifuged. The centrifugation time for separation is preferably 0.1 minutes or more, more preferably 0.5 minutes or more, preferably 150 minutes or less, and more preferably 120 minutes or less. ..

-Preparation process-
In the preparative step, the fibrous carbon nanostructure dispersion liquid is preparative as a supernatant liquid from the composition that has been allowed to stand or centrifuged in the separation step. Then, the supernatant liquid can be separated by collecting the supernatant liquid leaving a precipitate layer by, for example, decantation or pipetting. Specifically, for example, the supernatant liquid existing in the portion from the liquid surface of the composition after the separation step to a depth of 5/6 may be recovered.
The fibrous carbon nanostructure dispersion as the supernatant liquid separated from the composition after standing or centrifuging contains fibrous carbon nanostructures that did not precipitate by standing or centrifuging. By using this fibrous carbon nanostructure dispersion, it is possible to efficiently produce a self-supporting film having excellent light transmission.

[Light transmittance of dispersion]
Here, the light transmittance of the fibrous carbon nanostructure dispersion liquid at a wavelength of 550 nm is preferably 60% or more, more preferably 70% or more, still more preferably 80% or more. It is more preferably 85% or more, particularly preferably 88% or more, and preferably 99% or less. When the light transmittance of the dispersion liquid at a wavelength of 550 nm is 60% or more, a self-supporting film having excellent light transmittance can be efficiently produced. On the other hand, when the light transmittance of the dispersion liquid at a wavelength of 550 nm is 99% or less, the film strength of the obtained free-standing film can be sufficiently secured, and the handleability can be improved.
In the present invention, the "light transmittance of the fibrous carbon nanostructure dispersion liquid at a wavelength of 550 nm" can be measured by using the method described in the examples of the present specification.

[Supplying the dispersion liquid onto the support]
The method for supplying the above-mentioned fibrous carbon nanostructure dispersion liquid onto the support is not particularly limited, and examples thereof include coating and dropping. The support is not particularly limited as long as it can remove the solvent in the dispersion liquid to form a carbon film as a self-supporting film.

[Support]
For example, when the solvent in the dispersion liquid is removed by drying, examples of the support include a resin support and a glass support. Here, as the resin support, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polytetrafluoroethylene (PTFE), polyimide, polyphenylene sulfide, aramid, polypropylene, polyethylene, polylactic acid, polyvinyl chloride, polycarbonate, etc. Examples thereof include a support made of polymethyl methacrylate, an alicyclic acrylic resin, a cycloolefin resin, triacetyl cellulose and the like. Further, as the glass support, a support made of ordinary soda glass can be mentioned.
Further, for example, when the solvent in the dispersion liquid is removed by filtration, a porous support is used as the support. The porous support is not particularly limited, and examples thereof include filter paper and a porous sheet containing at least one of cellulose and nitrocellulose.

Further, the surface of the support to which the dispersion liquid is supplied (that is, the surface in contact with the free-standing film obtained after removing the solvent) preferably has a surface roughness Ra of 2.3 μm or less, preferably 2.0 μm or less. It is more preferably present, and further preferably 1.7 μm or less. If a support having a surface roughness Ra of 2.3 μm or less on the surface in contact with the free-standing film is used, the free-standing film can be easily peeled from the support in the self-supporting film peeling step described later. The lower limit of the surface roughness Ra is not particularly limited, but is usually 0.5 μm or more.

<< Laminated body forming process >>
In the laminate forming step, the solvent is removed from the dispersion liquid on the support to obtain a laminate having a self-supporting film and a support in contact with the self-supporting film.

[Removal of solvent]
Examples of the method for removing the solvent from the dispersion liquid include drying and filtration, but filtration is preferable from the viewpoint of easily and quickly removing the solvent.
As the filtration method, a known filtration method can be adopted. Specifically, as the filtration method, natural filtration, vacuum filtration, pressure filtration, centrifugal filtration and the like can be used. Among these, vacuum filtration is preferable.
It is not necessary to completely remove the solvent in the dispersion, and if the fibrous carbon nanostructures remaining after the removal of the solvent can be handled as a film-like aggregate (carbon film), some solvent may be used. There is no problem even if is left.

[Laminate]
The laminate of the present invention obtained by removing the solvent from the dispersion as described above may be immediately subjected to the self-supporting film peeling step described later, but the laminate is stored, transported, etc. in the state of the laminate. May be good. By storing and transporting the laminated body, damage to the self-supporting film can be prevented.

<< Self-supporting film peeling process >>
In the self-supporting film peeling step, the self-supporting film is peeled from the support by contacting the laminated body obtained in the laminated body forming step with ^{a stripping solution having an SP value of 10 (MPa) 1/2 or more.}

[Stripping liquid]
Here, the SP value of the stripping solution needs to be ^{10 (MPa) 1/2 or more.} If the SP value of ^{the stripping solution is less than 10 (MPa) 1/2,} it is presumed that the stripping solution does not sufficiently penetrate between the support and the free-standing film, but the free-standing film is peeled from the support without damage. It becomes difficult to do. The upper limit of the SP value of the stripping solution is not particularly limited, but is, for example, 25 (MPa) ^1/2 or less.

Here, as the liquid can be used as stripping solution, SP value of the entire stripping liquid is not particularly limited as long 10 ^{(MPa) 1/2} or more, SP value of 10 ^{(MPa) 1/2} or more liquids One kind may be used alone, a mixture of two or more kinds of liquids having an SP value of 10 (MPa) ^1/2 or more may be used, and one kind or two or more kinds of SP values may be used. A mixture of 10 (MPa) ^1/2 or more liquid and one or more liquids having an SP value of ^{less than 10 (MPa) 1/2} may be used.
Examples of the liquid having an SP value of 10 (MPa) ^1/2 or more include water (pure water, nanobubble water, etc.), ethanol, methanol, and isopropyl alcohol (IPA).

[Contact between laminate and release liquid]
The method of contacting the laminate with the release liquid having an SP value of 10 (MPa) ^1/2 or more is not particularly limited as long as the free-standing film can be removed without damage, but the laminate can be immersed in the release liquid. preferable. By immersing the laminate in the release liquid, the free-standing film can be satisfactorily peeled from the support in the release liquid, and the free-standing film after peeling can be recovered. In addition, the dispersant present in the free-standing film can be removed by immersing the laminate in the stripping solution. Here, the immersion conditions (for example, immersion time, immersion temperature) are not particularly limited as long as the support and the free-standing film can be satisfactorily peeled off.

Then, after peeling from the support, it can be arbitrarily dried to obtain the self-supporting film of the present invention having excellent light transmission.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, "%" and "part" representing quantities are based on mass unless otherwise specified.
Then, in the present invention, the G / D ratio of the carbon film and the fibrous carbon nanostructures, the light transmittance of the fibrous carbon nanostructure dispersion at a wavelength of 550 nm, the thickness of the carbon film, the surface resistance value and the light rays having a wavelength of 550 nm. The transmittance and the surface roughness Ra of the support were measured and evaluated as follows.

<G / D ratio>
Using a microlaser Raman spectrophotometer (Nicollet Almega XR manufactured by Thermo Fisher Scientific Co., Ltd.), Raman spectra of self-supporting membranes and fibrous carbon nanostructures were measured. Then, with respect to the obtained Raman spectrum, the intensity of the G band peak observed near ^{1590 cm -1 and the intensity of the D band peak observed near 1340 cm -1} were obtained, and the G / D ratio was calculated.
<Light transmittance of dispersion with a wavelength of 550 nm>
A measurement sample was prepared by dropping the dispersion liquid into a quartz cell having a width of 0.1 mm. Then, the light transmittance of the dispersion liquid at a wavelength of 550 nm was measured using a spectrophotometer (manufactured by JASCO Corporation, “V-670”).
<Thickness of carbon film>
The obtained carbon film is placed on a glass substrate, and "Dimension Icon AFM" (manufactured by Bruker) is used to measure the steps at any three points between the glass surface and the carbon film surface, and the average value is calculated as the carbon film. The thickness was set to.
<Surface resistance value of carbon film>
The sheet resistance of the carbon film was measured by the four-terminal four-probe method using a resistivity meter (“Loresta (registered trademark) GP” manufactured by Mitsubishi Chemical Corporation).
<Light transmittance of carbon film with wavelength of 550 nm>
The light transmittance of the carbon film at a wavelength of 550 nm was measured using a spectrophotometer (manufactured by JASCO Corporation, “V-670”).
<Surface roughness Ra of support>
Shape analysis A laser microscope (“VK-X160” manufactured by KEYENCE CORPORATION) is used to measure the surface roughness of any five points on the surface on the dispersion liquid supply side, and the average value is the surface roughness Ra (μm) of the support. And said.

(Example 1)
<Preparation of fibrous carbon nanostructure dispersion>
"MEIJO eDIPS" as a fibrous carbon nanostructure (manufactured by Meijo Nanocarbon, G / D ratio: 200, single-walled CNT) with respect to 500 mL of a 2% SDS aqueous solution containing sodium dodecylsulfonate (SDS) as a dispersant. Ratio: 90%, 3σ / Av: 0.5, average diameter (Av): 1.5 nm, BET specific surface area: 750 m ² / g) was added in an amount of 0.1 g, and fibrous carbon nanostructures, dispersants, and dispersants were added. The composition containing water is filled in a high-pressure homogenizer (manufactured by Migrain Co., Ltd., product name "BERYU SYSTEM PRO") having a multi-stage pressure control device (multi-stage step-down pressure device) that applies back pressure during dispersion, and at a pressure of 100 MPa. The composition was dispersed. Specifically, while applying back pressure, a shearing force was applied to the composition to disperse the fibrous carbon nanostructures. The dispersion treatment was carried out for 10 minutes while returning the dispersion liquid flowing out of the high-pressure homogenizer to the high-pressure homogenizer again (dispersion treatment step).
Next, 50 times the amount of water of the composition was added to the composition after the dispersion treatment. The obtained diluted solution was allowed to stand at room temperature (25 ° C.) for 2 hours (separation step). After standing for 2 hours, the supernatant was collected to obtain a fibrous carbon nanostructure dispersion (preparation step). The light transmittance of the obtained dispersion liquid (supernatant liquid) at a wavelength of 550 nm was 90.0%.
<Manufacturing of laminated body>
The dispersion obtained above was filtered using a vacuum filtration device equipped with a membrane filter (cellulose mixed ester type, surface roughness Ra of the surface on the dispersion supply side: 1.2 μm) as a porous support. The supernatant was filtered under the condition of 0.09 MPa to obtain a laminate having a carbon film on the membrane filter.
<Peeling of carbon film>
The laminate obtained above was immersed in a stripping solution (SP value: 10 (MPa) ^1/2 , composition: 50% water, 50% ethanol). After 2 minutes from the immersion, the carbon film peeled off from the membrane filter and floated on the liquid surface of the peeling liquid was recovered. The obtained carbon film had the same size as the membrane filter, and maintained the state of the film even when peeled from the membrane filter (that is, the obtained carbon film was a self-supporting film). The obtained carbon film (self-supporting film) has a G / D ratio of 21, a light transmittance of 92.7% at a wavelength of 550 nm, a surface resistance value of 500 Ω / □, and a thickness of 50 nm. It was.

(Example 2)
In the separation process, instead of separation by standing, centrifuge using a centrifuge (Sinky, "Awatori Rentaro") (under vacuum, centrifugal rotation speed: 50 rpm, centrifugation time: 1 minute) A fibrous carbon nanostructure dispersion, a laminate, and a carbon film (self-supporting film) were obtained in the same manner as in Example 1 except that separation was adopted. The light transmittance of the obtained dispersion liquid (supernatant liquid) at a wavelength of 550 nm was 98.6%. Further, the obtained carbon film had the same size as the membrane filter, and maintained the state of the film even when peeled from the membrane filter (that is, the obtained carbon film was a self-supporting film). The obtained carbon film (self-supporting film) had a G / D ratio of 21, a light transmittance of 95% at a wavelength of 550 nm, a surface resistance value of 500 Ω / □, and a thickness of 30 nm.

(Comparative Example 1)
As a fibrous carbon nanostructure, NC7000 (manufactured by Nanosil, G / D ratio: 1.2, single-walled CNT ratio: 0%, 3σ / Av: 0.5, average diameter (Av): 9.5 nm, BET A fibrous carbon nanostructure dispersion and a laminate were obtained in the same manner as in Example 1 except that the specific surface area: 250 m ^{2 / g) was used.} Then, an attempt was made to peel off the carbon film in the same manner as in Example 1, but since the film strength was extremely weak, the carbon film collapsed at the same time as being immersed in the stripping solution, and a carbon film as a self-supporting film could be obtained. could not.

According to the present invention, it is possible to provide a self-supporting film made of a plurality of fibrous carbon nanostructures having excellent light transmittance, a laminate having the self-supporting film, and a method for producing the self-supporting film. it can.

Claims (7)

It is a self-supporting film composed of multiple fibrous carbon nanostructures.
The ratio of G-band peak intensity to D-band peak intensity in the Raman spectrum (G / D ratio) is 2 or more, the light transmittance at a wavelength of 550 nm is 60% or more, and
The plurality of fibrous carbon nanostructures are self-supporting membranes containing single-walled carbon nanotubes. The self-supporting film according to claim 1, wherein the thickness is 10 nm or more and 110 nm or less. The self-supporting film according to claim 1 or 2, wherein the surface resistance value is 600 Ω / □ or less. The self-supporting film according to any one of claims 1 to 3, wherein the ratio (G / D ratio) of the G band peak intensity to the D band peak intensity in the Raman spectrum is 10 or more. The self-supporting film according to any one of claims 1 to 4,
A laminated body including a support in contact with the free-standing film. The laminate according to claim 5, wherein the surface roughness Ra of the surface of the support in contact with the free-standing film is 2.3 μm or less. The method for producing a self-supporting film according to any one of claims 1 to 4.
A fibrous form containing a plurality of fibrous carbon nanostructures containing single-walled carbon nanotubes and having a G-band peak intensity ratio (G / D ratio) of 2 or more to the D-band peak intensity in the Raman spectrum, and a solvent. The process of supplying the carbon nanostructure dispersion on the support,
A step of forming a laminate having a self-supporting film on the support by removing the solvent from the fibrous carbon nanostructure dispersion liquid on the support.
A step of peeling the self-supporting film from the support by contacting the laminated body with a stripping solution having an SP value of 10 (MPa) ^{1/2 or more.}
A method for producing a self-supporting film, including.