阅读说明：本技术 一种片材及其制造方法 (Sheet and manufacturing method thereof ) 是由 山岸智子 上岛贡 西内友也 高桥成彰 于 2018-09-21 设计创作，主要内容包括：本发明提供一种片材,其包含纤维状基材、以及附着于构成该纤维状基材的纤维的碳纳米管。而且,该片材所包含的碳纳米管的主成分为单层碳纳米管。(The present invention provides a sheet comprising a fibrous base material and carbon nanotubes attached to fibers constituting the fibrous base material. The sheet contains a single-walled carbon nanotube as a main component of the carbon nanotube.)

1. A sheet comprising a fibrous base material and carbon nanotubes attached to fibers constituting the fibrous base material, wherein the carbon nanotubes comprise single-walled carbon nanotubes as a main component.

2. The sheet according to claim 1, wherein the single-walled carbon nanotube has a BET specific surface area of 600m²More than g.

3. The sheet material of claim 1 or 2, wherein no binding material is present.

4. A sheet according to any one of claims 1 to 3, wherein the density is 0.20g/cm³Above and 0.80g/cm³The following.

5. The sheet according to any one of claims 1 to 4, wherein the carbon nanotube has a weight per unit area of 10g/m²The above.

6. The sheet according to any one of claims 1 to 5, wherein the electrical conductivity is 30S/cm or more.

7. A method for producing the sheet according to any one of claims 1 to 6, comprising:

will comprise a BET specific surface area of 600m²A carbon nanotube dispersion liquid preparation step of dispersing the carbon nanotubes of the single-walled carbon nanotubes in a dispersion medium to prepare a carbon nanotube dispersion liquid;

a contact step of contacting the fibrous base material with the carbon nanotube dispersion to obtain a primary sheet; and

a dispersion medium removing step of removing the dispersion medium from the primary sheet.

8. The method for producing a sheet according to claim 7, wherein the carbon nanotube dispersion used in the contacting step does not contain a binder.

Technical Field

The present invention relates to a sheet and a method for manufacturing the same. In particular, the present invention relates to a sheet comprising carbon nanotubes and a method for manufacturing the same.

Background

In recent years, carbon nanotubes (hereinafter, sometimes referred to as "CNTs") have attracted attention as a material that is lightweight and has excellent electrical conductivity, mechanical properties, and the like. However, since a fibrous carbon nanostructure such as CNT is a fine structure having a diameter of a nanometer size, handling property and processability are not necessarily good for a monomer. Therefore, for example, the following is proposed: a plurality of CNTs are attached to a substrate and formed into a sheet shape, and the sheet is applied to various uses. Examples of applications of such a sheet include electromagnetic wave absorption applications. As a specific sheet, for example, patent document 1 discloses a sheet in which a layer including a plurality of layers of carbon nanotubes, a binder, and the like is formed on the surface of a fibrous structure. For example, patent document 2 discloses a sheet in which a coating liquid containing a plurality of layers of carbon nanotubes and a resin component is applied to a substrate.

Disclosure of Invention

Problems to be solved by the invention

However, the sheet proposed in the above-mentioned conventional art still has room for improvement in terms of further improving the conductivity and sufficiently suppressing the carbon nanotubes from falling off from the sheet.

Accordingly, an object of the present invention is to provide a sheet containing carbon nanotubes, which has excellent electrical conductivity and in which carbon nanotubes are less likely to fall off.

Further, the present invention aims to provide a method for producing a sheet containing carbon nanotubes, which is excellent in electrical conductivity and in which carbon nanotubes are less likely to fall off, in a satisfactory manner.

Means for solving the problems

The present inventors have conducted intensive studies with a view to solving the above-mentioned problems. Then, the present inventors have found that a sheet formed by attaching carbon nanotubes containing a single-walled carbon nanotube as a main component to a fiber is excellent in electrical conductivity and can well hold the carbon nanotubes, thereby completing the present invention.

That is, the present invention has been made to solve the above-mentioned problems advantageously, and a sheet of the present invention is characterized by comprising a fibrous base material and carbon nanotubes attached to fibers constituting the fibrous base material, wherein the carbon nanotubes contain single-walled carbon nanotubes as a main component. Such a sheet has excellent conductivity, and the carbon nanotubes are less likely to fall off from the sheet.

In the present invention, the phrase "the carbon nanotube contains a single-walled carbon nanotube as a main component" means that the ratio of the mass of the single-walled carbon nanotube exceeds 50 mass% with the total mass of the carbon nanotubes contained in the sheet taken as 100 mass%.

In the sheet of the present invention, the BET specific surface area of the single-walled carbon nanotube is preferably 600m²More than g. If the BET specific surface area of the single-walled carbon nanotube is 600m²The electrical conductivity of the sheet can be further improved and the carbon nanotubes can be more effectively prevented from falling off from the sheet.

In the present invention, the "BET specific surface area" refers to a nitrogen adsorption specific surface area measured by the BET (Brunauer-Emmett-Teller) method.

Further, the sheet of the present invention preferably does not contain a binder (adhesive). If the sheet does not contain a binder, the conductivity of the sheet can be further improved.

Further, in the sheet of the present invention, the density is preferably 0.20g/cm³Above and 0.80g/cm³The following. Of sheets having a density in the above rangeThe conductive sheet is more excellent in conductivity, has a lower density than so-called buckypaper, and is easy to carry, for example, metal particles. In addition, in the present invention, the density of the sheet means the mass of the sheet per unit volume. The density of the sheet can be measured by the method described in the examples of the present specification.

In the sheet of the present invention, the weight per unit area of the carbon nanotubes is preferably 10g/m²The above. When the weight per unit area of the carbon nanotube is equal to or more than the lower limit, the electrical conductivity of the sheet can be further improved, and the mechanical strength of the sheet can be improved.

In the present invention, the weight per unit area of the carbon nanotube can be measured by the method described in the examples of the present specification.

The sheet of the present invention preferably has an electrical conductivity of 30S/cm or more. In addition, in the present invention, the "electrical conductivity" of the sheet can be determined according to jis k 7194: 1994, measured by the method described in the examples of this specification.

Further, in order to advantageously solve the above-mentioned problems, a method for producing a sheet according to the present invention is a method for producing a sheet, the method comprising: will comprise a BET specific surface area of 600m²A carbon nanotube dispersion liquid preparation step of dispersing the carbon nanotubes of the single-walled carbon nanotubes in a dispersion medium to prepare a carbon nanotube dispersion liquid; a contact step of contacting the fibrous base material with the carbon nanotube dispersion to obtain a primary sheet; and a dispersion medium removing step of removing the dispersion medium from the primary sheet. In the method for producing the sheet of the present invention, the BET specific surface area of 600m is used²The sheet can be produced well from a dispersion prepared from the single-walled carbon nanotubes of the concentration of the carbon nanotubes of the present invention.

In the method for producing a sheet of the present invention, the carbon nanotube dispersion used in the contacting step preferably does not contain a binder. By producing a sheet by contacting the fibrous base material with the carbon nanotube dispersion liquid containing no binder in the contacting step, the conductivity of the obtained sheet can be further improved.

Effects of the invention

According to the present invention, a sheet containing carbon nanotubes, which has excellent electrical conductivity and in which carbon nanotubes are less likely to fall off, can be provided.

Further, according to the present invention, there can be provided a production method capable of favorably producing a sheet containing carbon nanotubes which is excellent in electrical conductivity and in which carbon nanotubes are less likely to fall off.

Detailed Description

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

The sheet of the present invention is characterized by comprising a fibrous base material and carbon nanotubes attached to fibers constituting the fibrous base material, wherein the carbon nanotubes contain single-walled carbon nanotubes as a main component. The sheet of the present invention may optionally contain other components such as a binder, a carbon-based material other than carbon nanotubes, and an additive used in the production of the sheet. In the present specification, the term "carbon nanotube is attached" to a fiber constituting a fibrous base material means not only a state in which a layer containing a carbon nanotube is formed adjacent to the fibrous base material but also a state in which the carbon nanotube is attached to or entangled with the fiber constituting a constituent unit of the fibrous base material. In the sheet of the present invention, the following state is preferable: the carbon nanotubes are attached not only to the fibers located on the surface of the fibrous base material but also to the fibers located inside the fibrous base material. This is because, with such a structure, a conductive network communicating from one surface side to the other surface side of the sheet can be formed well, and the conductivity of the sheet is further improved.

The fibers constituting the fibrous base material constituting the sheet of the present invention are not particularly limited, and examples thereof include organic fibers. Examples of the organic fibers include synthetic fibers made of polymers such as polyvinyl alcohol, vinylon, polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, poly-e-caprolactone, polyacrylonitrile, polylactic acid, polycarbonate, polyamide, polyimide, polyethylene, polypropylene, polyethylene terephthalate, and modified products thereof; natural fibers such as cotton, flax, wool, and silk. As the synthetic fiber-forming polymer, one kind may be used alone, or a plurality of kinds may be used in combination. Among these, synthetic fibers are preferable as the fibers constituting the fibrous base material, and among these, polyethylene terephthalate and vinylon, which is an acetal of polyvinyl alcohol, are more preferable. The fibrous base material of the present invention may be a woven or nonwoven fabric made of these fibers. Among these, the fibrous base material of the present invention is preferably a nonwoven fabric. In the present specification, the term "nonwoven fabric" is used, for example, in JIS L0222: 2001, refers to "the product of fibers oriented in one direction or randomly with fibers bonded together by crossing and/or fusing and/or bonding between fibers in a fibrous sheet, web or batt", with the exception of paper, fabric, knits, tufting and shrink felts.

The air permeability of the fibrous substrate which may constitute the sheet of the present invention is preferably 5cc/cm²At least 500cc/cm in volume²The ratio of the water to the water is less than s. Further, the air permeability of the fibrous base material is more preferably 10cc/cm²300cc/cm and a volume of the catalyst²The ratio of the water to the water is less than s. By using a fibrous substrate having an air permeability of not less than the lower limit, CNTs can easily penetrate into the interior of the fibrous substrate, formation of a good conductive network can be promoted, and the conductivity of the sheet can be further improved. Further, by using a fibrous base material having an air permeability of not more than the above upper limit value, it is possible to inhibit CNTs that have entered the interior of the fibrous base material from falling off from the sheet, and to promote formation of a good conductive network, thereby further improving the conductivity of the sheet.

The Carbon Nanotubes (CNTs) contained in the sheet of the present invention contain single-walled carbon nanotubes (single-walled CNTs) as a main component. As a component other than the single-layer CNT that can be included in the CNT, a multi-layer carbon nanotube (multi-layer CNT) can be given. Here, the ratio of the single-layer CNTs to the total mass of the CNTs needs to be more than 50 mass%, preferably 90 mass% or more, more preferably 95 mass% or more, and may be 100 mass%. When the CNTs include a plurality of CNTs, the number of the CNTs is preferably 5 or less.

The reason why the sheet of the present invention can realize good conductivity and make CNTs difficult to fall off by attaching CNTs containing a single layer of CNTs as a main component to fibers constituting a fibrous substrate is not clear, but is presumed as follows. First, single-layer CNTs have high intrinsic conductivity compared to multi-layer CNTs. Therefore, if such a single-layer CNT is a main component of CNTs included in a sheet, electrical conductivity can be improved as compared with a sheet including CNTs mainly composed of multi-layer CNTs in the related art. Furthermore, the single-layer CNTs easily interact with each other and with other objects such as multi-layer CNTs and fibrous substrates. As a result of the interaction, CNTs can be firmly held by the fibrous substrate. Further, according to the study of the present inventors, it has been unexpectedly found that the CNT included in the sheet of the present invention is mainly composed of a single-layer CNT, and thus the uniformity of the thickness of the sheet can be improved.

Hereinafter, suitable properties of the CNT are described, and the properties are preferably applied to both the CNT used as a material in the production of the sheet of the present invention and the CNT included in the sheet of the present invention. More specifically, at least the BET specific surface area, the average diameter, and the like are not lower than the value of the BET specific surface area exhibited by the CNT as a material in principle even after various treatments included in a method for producing a sheet described later.

CNTs are not particularly limited, and can be produced by a known CNT synthesis method such as an arc discharge method, a laser ablation method, and a chemical vapor deposition method (CVD method). Specifically, CNTs can be efficiently produced, for example, by the following method: when CNTs are synthesized by a chemical vapor deposition method (CVD method) by supplying a raw material compound and a carrier gas to a substrate having a catalyst layer for producing carbon nanotubes on the surface thereof, the catalyst activity of the catalyst layer is dramatically improved by the presence of a small amount of an oxidizing agent (catalyst activating substance) in the system (supergrowth method; see international publication No. 2006/011655). In the following, the carbon nanotube obtained by the overgrowth method is sometimes referred to as "SGCNT".

Further, the CNT preferably shows an upwardly convex shape according to a t-curve obtained from an adsorption isotherm.

Here, the growth of the nitrogen adsorbing layer in a substance having fine pores on the surface is classified into the following processes (1) to (3). Then, the slope of the t-curve changes according to the following processes (1) to (3).

(1) Process for forming monomolecular adsorption layer on whole surface by nitrogen molecules

(2) Process for forming a multi-molecular adsorption layer and its accompanying capillary condensation filling in pores

(3) Process for forming a polymeric adsorbent layer on an apparently non-porous surface having pores filled with nitrogen

In the t-curve showing the upwardly convex shape, the curve is located on a straight line passing through the origin in a region where the average thickness t of the nitrogen adsorbing layer is small, whereas the curve is located at a position deviated downward from the straight line as t becomes larger. In the CNTs having such a t-curve shape, the ratio of the internal specific surface area of the CNTs to the total specific surface area is large, indicating that a large number of openings are formed in the CNTs, and as a result, when a dispersion is prepared using such CNTs, the CNTs in the dispersion become less likely to agglomerate, and a sheet that is homogeneous and from which the CNTs are less likely to fall off can be obtained.

The inflection point of the t-curve of the CNT is preferably in a range of 0.2. ltoreq. t (nm). ltoreq.1.5, more preferably in a range of 0.45. ltoreq. t (nm). ltoreq.1.5, and still more preferably in a range of 0.55. ltoreq. t (nm). ltoreq.1.0. With CNTs having an inflection point of the t-curve within such a range, in the case of preparing a dispersion using such CNTs, the CNTs in the dispersion become more difficult to agglomerate. As a result, when such a dispersion is used, a more homogeneous sheet in which CNTs are less likely to fall off can be obtained.

Here, the "position of the inflection point" is an intersection of the approximate straight line a in the process of (1) and the approximate straight line B in the process of (3).

Further, the ratio (S2/S1) of the internal specific surface area S2 to the total specific surface area S1 of the CNT obtained by the t-curve is preferably 0.05 to 0.30. With CNTs having a value of S2/S1 in such a range, in the case of preparing a dispersion using such CNTs, the CNTs in the dispersion become more difficult to agglomerate. As a result, a more homogeneous sheet in which CNTs are less likely to fall off can be obtained.

Here, the total specific surface area S1 and the internal specific surface area S2 of the CNT can be determined from the t-curve. Specifically, first, the total specific surface area S1 and the external specific surface area S3 can be obtained from the slopes of the approximate straight lines in the processes (1) and (3), respectively. Then, by subtracting the external specific surface area S3 from the total specific surface area S1, the internal specific surface area S2 can be calculated.

The total specific surface area S1 and the internal specific surface area S2 obtained by measuring the adsorption isotherm of the CNT, preparing a t-curve, and analyzing the t-curve can be calculated using, for example, "BELSORP (registered trademark) -mini" (manufactured by Japan Belle inc., which is a commercially available measuring apparatus.

Further, the BET specific surface area of CMT is preferably 600m²A value of at least one of,/g, more preferably 800m²A ratio of the total amount of the components to the total amount of the components is 2000m or more²A ratio of the total amount of the compound to the total amount of the compound is 1800m or less²A ratio of 1600m or less, preferably²The ratio of the carbon atoms to the carbon atoms is less than g. When the BET specific surface area is within the above range, the carbon nanotubes can be more effectively inhibited from falling off the sheet. The reason for this is not clear, but is presumed as follows. First, it is presumed that the use of CNTs having a BET specific surface area of not less than the lower limit can more effectively suppress the carbon nanotubes from falling off from the sheet by exerting an appropriate mutual adsorption between the CNTs and the fibrous substrate and between the CNTs. Further, it is assumed that CNTs having a high BET specific surface area are CNTs having a property of being easily exfoliated, such as a short length or a large number of "splits", and it is presumed that the use of CNTs having a BET specific surface area of the above upper limit or less can suppress inclusion of those CNTs having a property of being easily exfoliated in the sheet, and as a result, can more effectively suppress exfoliation of the carbon nanotubes from the sheet.

The average diameter of the CNTs is preferably 1nm or more, preferably 60nm or less, more preferably 30nm or less, and still more preferably 10nm or less.

The average length of the CNTs is preferably 10 μm or more, more preferably 50 μm or more, still more preferably 80 μm or more, preferably 600 μm or less, more preferably 500 μm or less, and still more preferably 400 μm or less.

When the dispersion is prepared using CNTs having an average diameter and/or average length within the above-described range, the CNTs in the dispersion become less likely to agglomerate, and a sheet that is more uniform and from which the CNTs are less likely to fall off can be obtained.

Furthermore, CNTs typically have aspect ratios (length/diameter) exceeding 10.

The average diameter, average length, and specific length of CNTs can be determined by measuring the diameter and length of 100 CNTs randomly selected using a scanning electron microscope or a transmission electron microscope.

From the viewpoint of further improving the conductivity of the sheet of the present invention, the sheet of the present invention preferably does not contain a binder. If the sheet of the present invention contains a binder, the binder may be a known adhesive resin such as a polyester resin.

The sheet of the present invention may contain additives and the like used in the production of the sheet. Examples of such additives include a dispersant that can be used for dispersing CNTs during sheet production. The dispersant is preferably removed in the sheet production process, and the sheet of the present invention preferably does not contain a dispersant.

The density of the sheet of the present invention is preferably 0.20g/cm³Above, more preferably 0.45g/cm³Above, preferably 0.80g/cm³Hereinafter, more preferably 0.75g/cm³The following. When the density of the sheet of the present invention is not less than the lower limit, the conductivity of the sheet can be further improved. Further, if the density is not more than the upper limit value, the sheet can be prevented from being excessively "jammed". This can be suitably used for applications in which a functional material for imparting a desired function to the sheet is supported. More specifically, as the functional material, for example, particles formed of a metal such as tin, platinum, gold, or palladium, a metal oxide such as silicon oxide, lithium oxide, or lithium titanate, or the like can be favorably supported in the voids included in the sheet of the present invention. The particle size of such particles is not particularly limited, and may be, for example, 5 μm or less.

The density of the sheet can be measured by the method described in the examples described later. The density of the sheet is calculated based on the total mass of the sheet including the fibrous base material and the carbon nanotubes. In other words, the density of the sheet can be controlled by adjusting the type of fibrous base material used and the weight per unit area of the carbon nanotubes to be described later.

In addition, the sheet of the present invention preferably has a weight per unit area of the carbon nanotubes of 10g/m²The above. When the weight per unit area of the carbon nanotube is equal to or more than the lower limit, the conductivity of the sheet can be further improved. In addition, the weight per unit area of the carbon nanotubes may be, for example, 100g/m²The following. The method of controlling the basis weight will be described later in relation to the method of producing the sheet.

Further, the sheet of the present invention preferably has an electrical conductivity of 30S/cm or more, more preferably 35S/cm or more. The sheet having an electrical conductivity of 30S/cm or more can exhibit sufficient electrical conductivity and can be suitably used as, for example, an electromagnetic wave absorbing material. In addition, the conductivity is the reciprocal of the resistivity. The electrical conductivity of the sheet can be controlled by, for example, changing the weight per unit area of the carbon nanotubes in the sheet and the type of carbon nanotubes used.

The sheet of the present invention can be produced favorably by the sheet production method of the present invention. The method for manufacturing the sheet of the present invention may include: will comprise a BET specific surface area of 600m²A CNT dispersion preparation step of dispersing CNTs of a single CNT layer in a dispersion medium to prepare a CNT dispersion; a contact step of contacting the fibrous substrate with the CNT dispersion to obtain a primary sheet; and a dispersion medium removing step of removing the dispersion medium from the primary sheet. In the method for producing the sheet of the present invention, the BET specific surface area of the powder mixture is 600m²CNT dispersion liquid prepared from CNT single-layer CNTs having a concentration of at least one kind of carbon atom per gram, and sheet formation using the CNT dispersion liquid as a fibrous substrate can produce a sheet having high conductivity and high CNT exfoliation resistance. Hereinafter, each step will be described in detail. The sheet of the present invention can be produced by various sheet production methods as long as the sheet can be produced by the above-described necessary and preferable configurations. Example (b)By forming a fibrous substrate using the fibers after the treatment of attaching CNTs to the fibers as described above, a sheet having the necessary and preferable configurations as described above can also be produced.

In the CNT dispersion preparation step, the CNT dispersion is prepared so as to have a BET specific surface area of 600m²The CNT dispersion is prepared by dispersing CNT of single CNT layer in/g or more in a dispersing agent. As the single-layer CNT and other CNTs that can be used, the single-layer CNT and multi-layer CNT described above can be used. The CNT may contain a single layer of CNTs as a main component. The dispersion medium is not particularly limited, and the following can be used: water, isopropanol, 1-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, toluene, tetrahydrofuran, ethyl acetate, acetonitrile, ethylene glycol, methyl isobutyl ketone, and butanol. Among them, water is preferably used as the dispersion medium.

In the CNT dispersion liquid preparation step, a dispersant may be added as an additive in order to improve the dispersibility of CNTs in the CNT dispersion liquid when the CNT dispersion liquid is prepared. The dispersant is not particularly limited, and for example: known surfactants such as sodium dodecylsulfate, sodium deoxycholate, sodium cholate and sodium dodecylbenzenesulfonate, and synthetic polymers or natural polymers that function as dispersants. The amount of the dispersant added can be set to a general range.

In addition, in the CNT dispersion liquid preparation step, after the CNTs are added to the dispersion medium containing the surfactant as described above to obtain a coarse dispersion liquid, a dispersion method capable of obtaining a cavitation effect and/or a dispersion method capable of obtaining a crushing effect as disclosed in international publication No. 2014/115560 is applied to the obtained coarse dispersion liquid, whereby a CNT dispersion liquid having good dispersibility of the CNTs can be obtained. The dispersion method is not limited to these 2 methods, and it is needless to say that a method of directly stirring with a stirrer can be applied.

The CNT dispersion liquid may optionally contain other components such as the binder, the carbon-based material other than the carbon nanotubes, and additives, and when added, the CNT dispersion liquid may be added with these optional components, for example. As described above, it is preferable that no binder be blended in the CNT dispersion liquid from the viewpoint of improving the conductivity of the resulting sheet.

The dispersion time in the CNT dispersion liquid preparation step can be, for example, 1 minute or more and 20 minutes or less.

In the contacting step, the fibrous substrate is contacted with the CNT dispersion to obtain a primary sheet in which CNTs are attached to or held on the fibrous substrate. The contacting method is not particularly limited as long as the CNT dispersion can be contacted with at least one surface, preferably both surfaces, of the fibrous substrate, and examples thereof include: a method of immersing the fibrous substrate in the CNT dispersion liquid, a method of coating the CNT dispersion liquid on the fibrous substrate, and the like. The conditions such as time and temperature required for the contact step are not particularly limited, and can be arbitrarily set according to the desired weight per unit area of the CNT. The CNT dispersion used in the contact step preferably does not contain a binder. That is, it is preferable that not only the CNT dispersion is not mixed with the binder in the dispersion preparation step as described above, but also the CNT dispersion is not mixed with the binder at any time from immediately after the dispersion preparation step to immediately before the contact step.

In the dispersion medium removing step, the dispersion medium is removed from the primary sheet. The method for removing the dispersion medium is not particularly limited, and any method for removing the dispersion medium can be used. Here, among the CNTs that the primary sheet may contain, there are CNTs that are held in the fibrous base material by direct or indirect interaction with the surface of the fibrous base material, and on the other hand, there may also be CNTs that are suspended in the dispersion medium remaining in the fibrous base material. The former CNTs are higher than the latter CNTs in terms of stable adhesion to the fibrous substrate. In the dispersion medium removing step, the latter CNTs can also be removed together with the dispersion medium. Alternatively, as a result of removing the dispersion medium in the dispersion medium removing step, the latter CNTs can be made to interact with at least one of the fibrous substrate and CNTs having high stable adhesion to the fibrous substrate. The conditions such as time and temperature of the dispersion medium removing step can be arbitrarily set depending on the type of the dispersion medium used and the shape of the fibrous base material.

After the dispersion medium removing step, the cleaning step can be optionally performed. By performing such a cleaning step, the dispersant can be removed from the sheet when the CNT dispersion contains the dispersant as an arbitrary component. Further, by performing the cleaning step under arbitrary conditions, the unit area weight can be adjusted to a desired amount. Further, by performing the cleaning step, CNTs having low stable adhesion to the fibrous substrate are removed, so that stable adhesion of CNTs remaining in the obtained sheet to the fibrous substrate can be improved, and the CNTs can be effectively prevented from falling off from the sheet.

In the washing, there is no particular limitation, and known organic solvents such as isopropyl alcohol and various solvents can be used as dispersion media usable in the preparation of the dispersion. Among them, water is preferably used. The cleaning method is not particularly limited, and examples thereof include: a method of bringing a CNT-adhered surface of a fibrous substrate into contact with a dispersion medium.

The conditions such as the number of times of cleaning and the cleaning temperature can be determined depending on the shape of the fibrous base material, the desired weight per unit area of the CNT, and the like.

Thereafter, a drying step is performed to dry the primary sheet, thereby obtaining the sheet of the present invention. The drying method is not particularly limited, and examples thereof include: hot air drying, vacuum drying, hot roll drying, infrared irradiation, and the like. The drying temperature is not particularly limited, and is usually from room temperature to 200 ℃ and is usually not less than 1 hour and not more than 48 hours.

The sheet of the present invention obtained as described above has excellent conductivity, and CNTs are less likely to detach.