WO2020195974A1 - Nanocarbon dispersion liquid, method for producing same, nanocarbon dispersing agent, and electromagnetic wave-shielding material - Google Patents

Abstract

The purpose of the present disclosure is to provide: (1) a dispersion liquid in which nanocarbon such as carbon nanotubes is stably dispersed and which exhibits good fluidity, and a method for producing same; (2) a nanocarbon dispersing agent that is added in order to obtain the dispersion liquid; and (3) an electromagnetic wave-shielding material. This nanocarbon dispersion liquid contains nanocarbon, cellulose nanocrystals and a dispersion medium.

Description

Nanocarbon dispersion liquid and its manufacturing method, nanocarbon dispersant and electromagnetic wave shielding material

The present disclosure relates to a nanocarbon dispersion liquid containing nanocarbon and cellulose nanocrystals, a method for producing the same, and a nanocarbon dispersant containing cellulose nanocrystals.

Since nanocarbons such as carbon nanotubes and nanographenes have high surface energy, a strong van der Waals force acts on the surface of the nanocarbons even if the nanocarbons are dispersed in the medium. Therefore, nanocarbons tend to aggregate. Therefore, it is required to stably disperse nanocarbon.

As a method for dispersing nanocarbons, a method for dispersing carbon nanotubes in which water is added to a crushed mixture obtained by crushing monosaccharide or low sugar crystals, carbon nanotubes, and a nonionic or anionic surfactant is disclosed. (See, for example, Patent Document 1). Further, a method for dispersing carbon nanotubes using carboxymethyl cellulose as a dispersant is disclosed (see, for example, Patent Document 2). Further, a method for dispersing carbon nanotubes using cellulose nanofibers as a dispersant is disclosed (see, for example, Patent Document 3). Further, a method of dispersing multi-walled carbon nanotubes having an average fiber outer diameter in the range of 50 to 110 nm with sodium carboxymethyl cellulose is disclosed (see, for example, Patent Document 4).

Japanese Unexamined Patent Publication No. 2008-230935 International Publication No. 2005/082775 International Publication No. 2014/115560 Japanese Unexamined Patent Publication No. 2016-028109

However, the method disclosed in Patent Document 1 has a problem that only a low-concentration carbon nanotube dispersion liquid having an upper limit value of about 5 g / L can be obtained. In addition, since a surfactant is used, the dispersion liquid tends to have a problem of foaming. In the method disclosed in Patent Document 2, since carboxymethyl cellulose is used, the viscosity of the dispersion tends to be high, and when it is attempted to be produced using a disperser, there is a problem that the disperser is blocked by the viscous dispersion. In the method disclosed in Patent Document 3, since cellulose nanofibers are used, the viscosity of the dispersion tends to be high, and the concentration of carbon nanotubes in the examples is only 0.05% by mass at the maximum. The method disclosed in Patent Document 4 can be applied only to multi-walled carbon nanotubes having a specific fiber diameter, and it is difficult to stably disperse carbon nanotubes having a fiber diameter of 50 nm or less and a small fiber diameter (large specific surface area). Met.

In view of these problems, the present disclosure is to obtain (1) a dispersion liquid in which nanocarbons such as carbon nanotubes are stably dispersed and have fluidity, a method for producing the dispersion liquid, and (2) a dispersion liquid. It is an object of the present invention to provide a nanocarbon dispersant to be added and (3) an electromagnetic wave shielding material.

As a result of diligent studies to solve the above problems, the present inventors have found that the above problems can be solved by using cellulose nanocrystals, and have completed the present invention.

The nanocarbon dispersion liquid according to the present invention is characterized by containing nanocarbon, cellulose nanocrystals, and a dispersion medium.

In the nanocarbon dispersion liquid according to the present invention, the concentration of the nanocarbon is preferably 1% by mass or more. Even if the concentration of nanocarbon is 1% by mass or more, the stability and fluidity of the nanocarbon dispersion can be improved.

In the nanocarbon dispersion liquid according to the present invention, the mass-based content ratio (nanocarbon: cellulose nanocrystal) of the nanocarbon and the cellulose nanocrystal is preferably 1: 0.1 to 1:10. The stability and fluidity of the nanocarbon dispersion can be improved.

In the nanocarbon dispersion liquid according to the present invention, the concentration of the nanocarbon is 1% by mass or more and 4% by mass or less, and the total concentration of the nanocarbon and the cellulose nanocrystal exceeds 1% by mass and 15% by mass. The following is preferable. Even if the concentration of nanocarbon is high, the stability and fluidity of the nanocarbon dispersion can be improved.

In the nanocarbon dispersion liquid according to the present invention, it is preferable that the dispersion medium is a polar solvent. A nanocarbon dispersion having higher dispersibility can be obtained.

In the nanocarbon dispersion according to the present invention, it is preferable that the polar solvent is alcohols, ketones, amides, water, or a mixture thereof. A nanocarbon dispersion having even higher dispersibility can be obtained.

The method for producing a nanocarbon dispersion according to the present invention is characterized in that a mixed solution containing nanocarbon, cellulose nanocrystals, and a dispersion medium is dispersed by a disperser.

In the method for producing a nanocarbon dispersion according to the present invention, it is preferable that the mixed solution is a mixed solution prepared by adding the cellulose nanocrystals to the dispersion medium, stirring the mixture, and then adding the nanocarbons. The compatibility between the dispersion medium and the nanocarbon is less likely to be impaired, and the nanocarbon is less likely to float on the dispersion medium.

In the method for producing a nanocarbon dispersion according to the present invention, it is preferable that the cellulose nanocrystal is a spray-dried product. It is possible to easily adjust the concentration of cellulose nanocrystals.

In the method for producing a nanocarbon dispersion liquid according to the present invention, it is preferable that the disperser is a homogenizer. A nanocarbon dispersion with more stable dispersibility can be obtained.

The nanocarbon dispersant according to the present invention is characterized by containing cellulose nanocrystals.

The electromagnetic wave shielding material according to the present invention has a base material and a coating layer provided on the surface of the base material, and the coating layer contains nanocarbon and cellulose nanocrystals in a mutually mixed state. It is characterized by.

The electromagnetic wave shielding material according to the present invention has the shape of a film, and the film is characterized by containing nanocarbon and cellulose nanocrystals in a mutually mixed state.

According to the present disclosure, (1) a dispersion liquid in which nanocarbons such as carbon nanotubes are stably dispersed and has fluidity and a method for producing the dispersion liquid, and (2) nanocarbon dispersion added to obtain the dispersion liquid. Agents and (3) electromagnetic wave shielding materials can be provided.

It is an image of the appearance of the dried film produced by drying the dispersion liquid 1. It is an image of the appearance of the dried film produced by drying the dispersion liquid 2. It is an image of the appearance of the dried film produced by drying the dispersion liquid 3. It is an image of the appearance of the dried film produced by drying the dispersion liquid 4. It is a graph which shows the change of transmission loss with respect to the frequency of electromagnetic wave 45MHz to 3GHz, and shows the comparison of the coated paper which different coating layers of a paper base material and a dispersion liquid. It is a graph which shows the change of transmission loss with respect to the frequency of electromagnetic wave 500MHz to 18GHz, and shows the comparison of the coated paper which different coating layers of a paper base material and a dispersion liquid. It is a graph which shows the change of the transmission loss at the frequency of 300MHz and 7GHz of the electromagnetic wave with respect to the mass ratio of CNT with respect to the total mass of CNT and CNC. It is a graph which shows the change of transmission loss with respect to the frequency of electromagnetic wave 45MHz to 3GHz, and shows the comparison of the coating paper which the thickness of the coating layer of a paper base material and a dispersion liquid is different. It is a graph which shows the change of transmission loss with respect to the frequency of electromagnetic wave 500MHz to 18GHz, and shows the comparison of the coating paper which the thickness of the coating layer of a paper base material and a dispersion liquid is different. It is a graph which shows the change of the transmission loss at the frequency of 300MHz of the electromagnetic wave with respect to the thickness of the coating layer of a dispersion liquid, and the thickness of a dry film. It is a graph which shows the change of the transmission loss at the frequency 7GHz of an electromagnetic wave with respect to the thickness of the coating layer of a dispersion liquid, and the thickness of a dry film. It is a graph which shows the change of the transmission attenuation rate with respect to the frequency of the electromagnetic wave 500MHz to 18GHz, and shows the comparison of the coated paper which the thickness of the coating layer of a paper base material, aluminum foil and a dispersion liquid is different.

Next, the present invention will be described in detail by showing embodiments, but the present invention is not construed as being limited to these descriptions. The embodiments may be modified in various ways as long as the effects of the present invention are exhibited.

(Nanocarbon dispersion)
The nanocarbon dispersion liquid according to the present embodiment contains nanocarbon, cellulose nanocrystals, and a dispersion medium.

In the present embodiment, the nanocarbon refers to nanocarbon such as carbon nanotubes (hereinafter, also referred to as CNT), fullerenes, graphene nanoplatelets by a CVD method or a mechanical peeling method. These nanocarbons may have a single layer or a structure having two or more layers. In the present embodiment, these nanocarbon dispersions will be described, but the CNT dispersion will be described in detail below as a representative example.

Since CNT has an intermediate conductivity between that of fullerene and that of graphene, it has a feature that it is easy to use industrially. As the CNT, those having different fiber lengths, fiber diameters and BET specific surface areas are used depending on the application. For example, the fiber length range is 1 μm to 500 μm, and the fiber diameter range is 0.4 nm to 150 nm. Yes, the range of BET specific surface area is 10 m ² / g to 2500 m ² / g. In general, those having a small specific surface area have a large fiber diameter and are relatively easy to disperse, but as the specific surface area increases (as the fiber diameter decreases), dispersion tends to become difficult. Some CNTs have a functional group such as a carboxyl group introduced on the surface in order to improve dispersibility, but even in such a CNT, as the specific surface area increases (as the fiber diameter decreases), the CNTs disperse. Tends to be difficult. Specifically, when the BET specific surface area of the CNT into which a functional group such as a carboxyl group has been introduced exceeds 100 m ² / g, it may be difficult to sufficiently disperse the CNT with a conventional dispersant such as carboxymethyl cellulose. In particular, it has become difficult to obtain a dispersion having a high concentration, and it has been difficult to obtain a dispersion having a CNT concentration of more than 1% by mass.

Therefore, in the present embodiment, CNTs are dispersed by using cellulose nanocrystals (hereinafter, also referred to as CNC) as a dispersant. Here, the CNC is an acicular crystal obtained by subjecting a plant-derived cellulose fiber, particularly a wood-derived cellulose fiber, to a chemical treatment such as acid hydrolysis. Generally, the number average fiber diameter of CNC is 4 nm to 70 nm, the number average fiber length is 25 nm to 1000 nm, the BET specific surface area is 100 m ² / g to 500 m ² / g, and the aspect ratio is less than 50. is there. Here, the aspect ratio is a dimensionless number obtained by dividing the number average fiber length by the number average fiber diameter. Cellulose nanocrystals are also called cellulose nanowhiskers. In addition to CNC, cellulose nanofibers (hereinafter, also referred to as CNF) are known as dispersants. CNF has a number average fiber diameter equivalent to that of CNC, but has a fiber length longer than that of CNC. It refers to a fibrous material having a fiber length of 10 times or more, generally 5 μm or more, and a CNC aspect ratio of more than 100. On the other hand, CNC is an acicular crystal and does not have a large aspect ratio like a fibrous material such as CNF. However, in the present embodiment, the major axis of CNC is also referred to as fiber length, and the minor axis is also referred to as fiber diameter.

In order to obtain a dispersion liquid having a relatively high concentration of CNT, CNC having a fiber length shorter than that of CNF is suitable. In the present embodiment, the number average fiber length of the CNC is preferably 25 nm to 500 nm, more preferably 100 nm to 400 nm, and most preferably 200 nm to 300 nm. If the average fiber length is less than 25 nm, the CNCs may aggregate with each other. If the number average fiber length exceeds 500 nm, the viscosity of the dispersion liquid tends to increase, and the fluidity of the dispersion liquid tends to be impaired when the concentration of CNTs is increased. Since the fiber length of CNF is too long, not only is it difficult to disperse CNTs, but also the fluidity of the dispersion liquid is likely to be significantly impaired. For example, the viscosity measured with a B-type viscometer (20 ° C., 60 rpm, rotation time 1 minute) is 100 mPa · s or less in the case of a 2% by mass aqueous solution of CNC, and the fluidity is good, but CNF 2 The mass% aqueous solution often exceeds 10,000 mPa · s, resulting in impaired fluidity.

In the present embodiment, the number average fiber diameter of the CNC is preferably 5 nm to 60 nm, more preferably 10 nm to 50 nm, and most preferably 20 nm to 30 nm. If the average fiber diameter is less than 5 nm, the CNCs may aggregate with each other. If the number average fiber diameter exceeds 60 nm, the viscosity of the dispersion liquid may increase and the fluidity may decrease.

In the present embodiment, BET specific surface area of the CNC is ^{preferably 120m 2 / g ~ 400m 2 /} g, more preferably ^{150m 2 / g ~ 300m 2 /} g, and most preferably 175m ² / g ~ 250m ² / g. If the BET specific surface area is less than 120 m ² / g, the viscosity of the dispersion may increase and the fluidity may decrease. If the BET specific surface area exceeds 400 m ² / g, the viscosity of the dispersion becomes high, and CNCs may aggregate with each other.

In the present embodiment, the aspect ratio of the CNC is preferably 5 to 40, more preferably 10 to 30, and most preferably 15 to 25. If the aspect ratio is less than 5, the CNCs may aggregate with each other. If the aspect ratio exceeds 40, the fluidity of the dispersion liquid when the CNT concentration is increased may decrease.

The number average fiber diameter and number average fiber length of CNC can be calculated according to the following. Using a transmission electron microscope (TEM, Transmission Electron Microscope) or a scanning electron microscope (SEM, Scanning Electron Microscope) on the surface of the CNC, at least three images of the CNC surface where the fields of view do not overlap are taken. To do. For the obtained image, two random axes are drawn vertically and horizontally for each image, and the fiber diameter and fiber length of the fibers intersecting the axes are visually read. At this time, the magnification is 5,000 times, 10,000 times, or 50,000 times depending on the size of the constituent fibers. The condition for the number of fibers intersecting the two axes is 20 or more. Read the fiber diameter and fiber length values of the fibers that intersect each of the two axes. Therefore, information on at least 20 fibers × 2 × 3 = 120 fibers can be obtained. The number average fiber diameter and the number average fiber length are calculated from the fiber diameter and fiber length data thus obtained. The same applies to the case of calculating the number average fiber diameter and the number average fiber length of CNTs.

In this embodiment, for example, CNC prepared by a chemical method such as acid hydrolysis using a strong acid with sulfuric acid, hydrochloric acid, hydrobromic acid or the like can be used for an aqueous suspension or slurry of cellulose fibers. .. The strong acid is preferably sulfuric acid. Negative charge is given by adding a sulfate ester group to the surface by hydrodispersing with sulfuric acid, and since the sulfate ester group has a large molecular weight, it also causes steric hindrance and has a large ability to disperse CNT. It is presumed that it will be.

The degree of polymerization of CNC is not particularly limited, but is preferably 100 to 500, and more preferably 200 to 400. If the degree of polymerization is less than 100, the dispersibility of CNTs may decrease. If the degree of polymerization exceeds 500, the viscosity of the dispersion liquid may increase and the fluidity may decrease.

The details of the CNT dispersion have been described as a typical example of the nanocarbon dispersion, but even if the nanocarbon is another nanocarbon such as fullerene or graphene nanoplatelet, it is as good as the case of CNT. Nanocarbon dispersion can be obtained.

In the nanocarbon dispersion liquid of the present embodiment, by using such CNC as a dispersant, nanocarbons such as CNTs are stably dispersed in a dispersion medium. In particular, even nanocarbons having a BET specific surface area of 100 m ² / g or more, for example, CNTs having a BET specific surface area of 100 to 1000 m ² / g can be stably dispersed. It is considered that the fiber diameter of CNTs having a BET specific surface area of 100 to 1000 m ² / g is 30 nm or less, and many CNTs having such a fiber diameter are flexible and have excellent conductivity.

In this embodiment, the concentration of nanocarbon is preferably 1% by mass or more. Even if the concentration of nanocarbon is 1% by mass or more, the stability and fluidity of the dispersion liquid of nanocarbon can be improved.

In the nanocarbon dispersion liquid according to the present embodiment, the content ratio of nanocarbon and CNC in the nanocarbon dispersion liquid is not particularly limited, but in order to obtain a dispersion liquid in which nanocarbon is stably dispersed, a mass standard is used. Therefore, nanocarbon: cellulose nanocrystal = 1: 0.1 to 1:10 is preferable. More preferably, nanocarbon: cellulose nanocrystal = 1: 0.5 to 1: 5. Even if the content ratio contains less cellulose nanocrystals than 1: 0.1 (for example, nanocarbon: cellulose nanocrystals = 1: 0.01), it is effective in improving the dispersibility of nanocarbons. However, when the concentration of nanocarbon is relatively high, for example, 1% by mass or more, sediment may easily occur. On the other hand, when the content ratio contains more CNC than 1:10, the amount of nanocarbon is relatively small with respect to CNC, so that the effect of improving the dispersibility and stability of the nanocarbon dispersion has reached a plateau. Become. The upper limit of the concentration of nanocarbon is, for example, 4% by mass from the viewpoint of dispersibility.

In the nanocarbon dispersion liquid according to the present embodiment, the total concentration of nanocarbon and cellulose nanocrystals is preferably more than 1% by mass and 15% by mass or less. More preferably, it is 1.5% by mass or more and 13% by mass or less. Most preferably, it is 1.8% by mass or more and 5% by mass or less. If this total concentration is 1% by mass or less, nanocarbon may not be dispersed. If this total concentration exceeds 15% by mass, the viscosity of the dispersion liquid may increase and the fluidity may decrease.

In the nanocarbon dispersion liquid according to the present embodiment, the concentration of nanocarbon is 1% by mass or more and 4% by mass or less, and the total concentration of nanocarbon and cellulose nanocrystals is more than 1% by mass and 15% by mass or less. It is preferable to have. More preferably, the concentration of nanocarbon is 1% by mass or more and 3.5% by mass or less, and the total concentration of nanocarbon and cellulose nanocrystal is 1.5% by mass or more and 13% by mass or less. Most preferably, the concentration of nanocarbon is 1% by mass or more and 3% by mass or less, and the total concentration of nanocarbon and cellulose nanocrystal is 1.8% by mass or more and 5% by mass or less. Even if the concentration of nanocarbon is high, the stability and fluidity of the nanocarbon dispersion can be improved.

The dispersion medium can be arbitrarily selected depending on the intended use, but in order to fully exert the dispersion effect of CNC, it is preferable that the dispersion medium is a polar solvent in the nanocarbon dispersion liquid according to the present embodiment. ..

In the nanocarbon dispersion according to the present embodiment, the polar solvent is preferably alcohols such as methanol and ethanol; ketones such as acetone and methyl ethyl ketone, amides such as N-methylpyrrolidone, water, or a mixture thereof. .. Water is particularly preferable. A nanocarbon dispersion having even higher dispersibility can be obtained.

The nanocarbon dispersion can contain various additives as long as the desired effect of the present invention is not impaired. Additives include, for example, antioxidants, heat stabilizers, light stabilizers, UV absorbers, pigments, colorants, foaming agents, antistatic agents, flame retardants, lubricants, softeners, tackifiers, plasticizers, mold release agents. Agents, deodorants, fragrances or combinations thereof. Care must be taken when adding these additives, as they can affect the properties of nanocarbons. The nanocarbon dispersion liquid according to the present embodiment can be applied to a substrate such as a film, dried and formed into a film, and the solvent can be directly removed from the dispersion liquid or put into a poor solvent. A carbon nanotube / cellulose nanocrystal composite material can also be obtained by precipitating the solid content, filtering and drying. Examples of the surfactant include a surfactant having a defoaming effect, a surfactant having a dispersing effect, and a surfactant having a viscosity adjusting effect. In the present embodiment, the surfactant having a dispersing effect is used. It is preferable not to contain it. Surfactants with a dispersing effect can cause foaming.

(Manufacturing method of nanocarbon dispersion)
The method for producing a nanocarbon dispersion liquid according to the present embodiment is characterized in that a mixed liquid containing nanocarbon, cellulose nanocrystals, and a dispersion medium is dispersed by a disperser.

CNC includes, for example, a slurry product dispersed in water and a spray-dried product obtained by drying the slurry product, both of which can be used. In this embodiment, it is preferable that the CNC is a spray-dried product. Unlike CNF, CNC can be dispersed in water relatively easily even if it is a dried product, so that the concentration can be easily adjusted by using the dried product.

The order of addition of nanocarbon and CNC to the dispersion medium is not particularly limited, but in the method for producing a nanocarbon dispersion liquid according to the present embodiment, the mixed liquid simultaneously adds nanocarbon and CNC to the dispersion medium. It is preferable that the mixture is prepared by adding CNC to a dispersion medium and stirring, and then adding nanocarbon. Since nanocarbon has strong hydrophobicity, when the dispersion medium is water, if it is first added to the dispersion medium alone, it may float on the dispersion medium and easily impair compatibility. The fluidity of the mixed solution varies depending on the total concentration of nanocarbon and CNC and the content ratio based on mass. For example, when CNT: CNC = 1: 1 on a mass basis, the total concentration of CNT and CNC is 2 to 2. When it is set to 6% by mass, it is suitable for the dispersion treatment in the next step while maintaining an appropriate fluidity.

The disperser used for the dispersion treatment is not particularly limited, and various known mechanical dispersion treatment machines can be used. For example, a stirrer equipped with an agitator, an ultrasonic disperser, a high shear stirrer, a biomixer or a homogenizer can be used. Can be used. Two or more kinds of these dispersers may be used in combination. For example, the mixed solution is pre-dispersed with an ultrasonic disperser and then dispersed with a homogenizer, the mixed solution is pre-dispersed with a biomixer, and then dispersed with a homogenizer. Dispersion processing of steps or more may be performed.

In the method for producing a nanocarbon dispersion liquid according to the present embodiment, it is preferable that the disperser is a homogenizer. By performing the dispersion treatment with a homogenizer, a more stable nanocarbon dispersion can be obtained. Further, the homogenizer includes, for example, an ultrasonic type, a stirring type, and a high pressure type, and a high pressure type homogenizer (high pressure homogenizer) is preferable. Further, among the high pressure homogenizers, the water jet method is preferable. As a water jet type high pressure homogenizer, for example, there is Starburst (registered trademark) manufactured by Sugino Machine Limited. The pressure homogenized dispersion treatment condition is preferably a pressure of 100 to 250 MPa and 1 to 10 passes. A nanocarbon dispersion cannot be obtained without dispersion treatment. If the pressure is less than 100 MPa, the dispersion may be insufficient. If the pressure exceeds 250 MPa or the number of passes exceeds 10, the dispersion does not proceed and the high temperature of the dispersion liquid may rise.

(Nanocarbon dispersant)
The nanocarbon dispersant is an agent for dispersing nanocarbon. The nanocarbon dispersant according to the present embodiment contains cellulose nanocrystals. Examples of the form of the nanocarbon dispersant include a slurry product in which cellulose nanocrystals are dispersed in water (hereinafter referred to as Form L), and a spray-dried product of cellulose nanocrystals obtained by drying the slurry product (hereinafter referred to as Form L). Hereinafter, there is a dispersion liquid (hereinafter, referred to as Form N) in which the dispersion medium of the slurry product is replaced with a dispersion medium other than water. When the nanocarbon dispersant is in the form L, the nanocarbon dispersion liquid in which the dispersion medium is water can be easily prepared by adding the nanocarbon to the slurry product in the form L. When the nanocarbon dispersant is in the form M, the form of use is, for example, adding nanocarbon and the nanocarbon dispersant to the dispersion medium at the same time, or in a liquid in which the nanocarbon is dispersed in the dispersion medium. Nanocarbon dispersants may be added. Here, if the dispersion medium is water, it is preferable to add the nanocarbon and the nanocarbon dispersant to the dispersion medium at the same time from the viewpoint of the hydrophobicity of the nanocarbon. When the nanocarbon dispersant is of form N, by adding nanocarbon to the dispersion of form N, a nanocarbon dispersion in which the dispersion medium is a dispersion medium other than water can be easily prepared.

(Electromagnetic wave shielding material having a base material and a coating layer)
The electromagnetic wave shielding material according to the present embodiment has a base material and a coating layer provided on the surface of the base material, and the coating layer contains nanocarbon and cellulose nanocrystals in a mutually mixed state. ..

The base material is, for example, a plate or non-woven fabric made of paper, rubber, or resin. The material of the base material can be changed according to the form of the electromagnetic wave shielding material.

The base material has a single layer or a plurality of layers. As a form of the plurality of layers, for example, there is a paper in which a pigment coating layer is provided on a high-quality paper which is a support, or a laminated paper which is made by laminating.

The thickness of the coating layer is preferably 0.1 μm to 15.0 μm, more preferably 2.0 μm to 10.0 μm, and further preferably 3.5 μm to 5.0 μm. If it is less than 0.1 μm, the electromagnetic wave shielding property of the electromagnetic wave shielding material may not be sufficiently obtained. If it is larger than 15.0 μm, it may be difficult to prepare an electromagnetic wave shielding material.

If a filter paper or non-woven fabric that the dispersion liquid easily permeates is selected as the base material, the dispersion liquid will be impregnated into the base material. Then, when the dispersion medium of the dispersion liquid evaporates, a coating layer is formed on the inner wall of the base material. In this case, even if the thickness of the coating layer is small, there is a possibility that the electromagnetic wave shielding property can be imparted if the base material is sufficiently impregnated with the dispersion liquid. For example, when the dispersion liquid permeates substantially uniformly in the thickness direction of the base material and the permeation depth into the base material exceeds 10.0 μm, electromagnetic wave shielding property can be imparted even if the thickness of the coating layer is small. there is a possibility. The depth at which the coating layer is present is preferably 1.0 μm to 15.0 μm, more preferably 2.0 μm to 10.0 μm.

In the mixed state, for example, the nanocarbons in the coating layer are unevenly distributed and the cellulose nanocrystals are unevenly distributed, the nanocarbons are uniformly distributed, and the cellulose nanocrystals are unevenly distributed. A state, a state in which nanocarbons are unevenly distributed and cellulose nanocrystals are uniformly distributed, or a state in which nanocarbons are uniformly distributed and cellulose nanocrystals are uniformly distributed. Preferably, the nanocarbons in the coating layer are uniformly distributed and the cellulose nanocrystals are uniformly distributed.

The mass-based content ratio of nanocarbon and cellulose nanocrystals contained in the coating layer is preferably nanocarbon: cellulose nanocrystals = 1: 0.1 to 1:10, and more preferably 1: 0.1 to 1. It is 1: 5, and more preferably 1: 1. An electromagnetic wave shielding material having a high electromagnetic wave shielding property can be obtained.

The electromagnetic wave shielding material can be produced by applying a nanocarbon dispersion liquid to a base material, evaporating the dispersion medium contained in the nanocarbon dispersion liquid, and providing a coating layer. Here, the mass-based content ratio of the nanocarbon and the cellulose nanocrystal contained in the coating layer is the same as the mass-based content ratio of the nanocarbon and the cellulose nanocrystal contained in the nanocarbon dispersion. ..

(Electromagnetic wave shielding material with film shape)
The electromagnetic wave shielding material according to the present embodiment has the shape of a film, and the film contains nanocarbon and cellulose nanocrystals in a mutually mixed state.

The thickness of the film is preferably 30 μm to 160 μm, more preferably 40 μm to 160 μm. If it is less than 30 μm, it may be necessary to increase the CNT concentration contained in the film in order to obtain sufficient electromagnetic wave shielding property. If it is larger than 160 μm, the electromagnetic wave shielding property of the electromagnetic wave shielding material is saturated, and the thickened electromagnetic wave shielding property may not be improved.

The mixed state is, for example, a state in which nanocarbons in the film are unevenly distributed and cellulose nanocrystals are unevenly distributed, a state in which nanocarbons are uniformly distributed and cellulose nanocrystals are unevenly distributed. It is a state in which nanocarbons are unevenly distributed and cellulose nanocrystals are uniformly distributed, or a state in which nanocarbons are uniformly distributed and cellulose nanocrystals are uniformly distributed. Preferably, the nanocarbons in the film are uniformly distributed and the cellulose nanocrystals are uniformly distributed.

The mass-based content ratio of nanocarbon and cellulose nanocrystals contained in the film is preferably nanocarbon: cellulose nanocrystals = 1: 0.1 to 1:10, more preferably 1: 1 to 1:10. is there. The nanocarbons in the film can be uniformly distributed, and the cellulose nanocrystals can be uniformly distributed.

The electromagnetic wave shielding material can be produced by evaporating the dispersion medium contained in the nanocarbon dispersion liquid. Here, the mass-based content ratio of the nanocarbon and the cellulose nanocrystal contained in the film is the same as the mass-based content ratio of the nanocarbon and the cellulose nanocrystal contained in the nanocarbon dispersion.

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 the amount are based on mass unless otherwise specified.

(Manufacturing of CNC)
A sheet of coniferous sulfite pulp is roughly crushed by a dry method to obtain cotton-like fibers, and cotton-like fibers are added to a 64% sulfuric acid aqueous solution so that the solid content concentration of the cotton-like fibers becomes 3% by mass. A suspension was prepared and the cotton fibers were hydrolyzed in the suspension at 45 ° C. for 60 minutes. The operation of diluting the first suspension with ion-exchanged water 5-fold, allowing the suspension to settle and removing the supernatant was repeated until the pH of the supernatant became 5 or higher. The obtained suspension was concentrated by centrifugation, and then ion-exchanged water was added to adjust the solid content concentration to 2% by mass to obtain a second suspension. The second suspension was defibrated by an ultrasonic homogenizer (US300E, manufactured by Nippon Seiki Seisakusho), and then water was removed by a spray dry method to obtain a powdery CNC.

(CNT)
The carbon nanotubes used in each Example and Comparative Example are as follows. Each carbon nanotube is a commercially available product.
CNT (A): Carbon nanotube (trade name: K-nanos100P, multi-walled CNT, manufactured by Kumho Petrochemical, fiber length (Bundle Diameter) 3 μm, fiber diameter 8 to 15 nm, specific surface area 220 m ² / g)
CNT (B): Carbon nanotube (trade name: nanocil-7000, multi-walled CNT, manufactured by nanocil, number average fiber length 1.5 μm, number average fiber diameter 9.5 nm, specific surface area 250 to 300 m ² / g)

(Example 1)
The obtained CNC was added to ion-exchanged water as a dispersant and stirred, and then CNT (A) was gradually added together with ion-exchanged water to obtain a mixed solution. The concentration of CNC in the mixed solution was 2% by mass, and the concentration of CNT (A) was 2% by mass. The obtained mixed solution was dispersed for 30 minutes using a biomixer (BM-2 type, Nissei Tokyo Office), filtered through a 60-mesh sieve, and then a high-pressure homogenizer (trade name: Ultimizer, manufactured by Sugino Machine Limited). A carbon nanotube dispersion was obtained by passing the mixture 10 times at a pressure of 200 MPa.

(Example 2)
A carbon nanotube dispersion was obtained in the same manner as in Example 1 except that CNC was added so that the concentration of CNC in the mixed solution was 0.2% by mass.

(Example 3)
A carbon nanotube dispersion was obtained in the same manner as in Example 1 except that CNC was added so that the concentration of CNC in the mixed solution was 10% by mass.

(Example 4)
Same as in Example 1 except that CNT (A) was added so that the concentration of CNT (A) in the mixed solution was 1% by mass, and CNC was added so that the concentration of CNC was 1% by mass. A carbon nanotube dispersion was obtained.

(Example 5)
Same as in Example 1 except that CNT (A) was added so that the concentration of CNT (A) in the mixed solution was 1% by mass, and CNC was added so that the concentration of CNC was 0.1% by mass. A carbon nanotube dispersion was obtained.

(Example 6)
Same as in Example 1 except that CNT (A) was added so that the concentration of CNT (A) in the mixed solution was 1% by mass, and CNC was added so that the concentration of CNC was 10% by mass. A carbon nanotube dispersion was obtained.

(Example 7)
Change CNT (A) to CNT (B), add CNT (A) so that the concentration of CNT (B) in the mixed solution is 1.5% by mass, and the concentration of CNC is 1.5% by mass. A carbon nanotube dispersion was obtained in the same manner as in Example 1 except that CNC was added so as to become.

(Comparative Example 1)
Carbon nanotubes in the same manner as in Example 1 except that the CNC was changed to cellulose nanofibers obtained by mechanically defibrating hardwood kraft pulp (processing machine: Super Mascoroider, manufactured by Masuko Sangyo Co., Ltd.). A dispersion was obtained.

(Comparative Example 2)
The treatment was carried out in the same manner as in Example 1 except that the CNC was changed to carboxymethyl cellulose (CMC, cellogen PR, manufactured by Dai-ichi Kogyo Seiyaku), but the viscosity increased during the high-pressure homogenizer treatment, and the inside of the high-pressure homogenizer was blocked for the purpose. It was not possible to obtain the carbon nanotube dispersion liquid.

(Comparative Example 3)
CNC was changed to carboxymethyl cellulose (CMC, cellogen WS-C, manufactured by Dai-ichi Kogyo Seiyaku), and CNT (A) was added so that the concentration of CNT (A) in the mixed solution was 1.5% by mass. The treatment was carried out in the same manner as in Example 1 except that carboxymethyl cellulose was added so that the concentration of carboxymethyl cellulose became 1.5% by mass, but the viscosity increased during the high-pressure homogenizer treatment, and the inside of the high-pressure homogenizer was blocked for the purpose. It was not possible to obtain the carbon nanotube dispersion liquid.

(Comparative Example 4)
A carbon nanotube dispersion was obtained in the same manner as in Example 1 except that CNC was not added to the mixed solution.

(Comparative Example 5)
The same as in Example 1 except that the CNC was changed to a surfactant having a dispersing effect (sodium dodecyl sulfate, manufactured by Tokyo Chemical Industry Co., Ltd.), but a large amount of bubbles were generated at the stage of the dispersion treatment with the biomixer. , The treatment with the high pressure homogenizer could not be performed.

Table 1 shows the composition and evaluation of the nanocarbon dispersions obtained in each Example and Comparative Example. The following methods were used for the evaluation of the nanocarbon dispersion.

(Dispersiveness)
The nanocarbon dispersion obtained by the dispersion treatment was diluted with ion-exchanged water so that the CNT concentration was 0.05% by mass, left in a glass vial for 1 hour, and then evaluated by visual observation according to the following criteria. ..
A: It is good because there is no sedimentation of aggregates and separation of CNT and water.
B: There is no sedimentation of aggregates, and the separation between CNT and water is slight and good.
C: There are fine aggregates, and a small separation between CNT and water can be confirmed (lower limit of practical use).
D: Most of the agglomerates are large, and the separation from water is also large (not practical).

(Liquidity)
The viscosity of the nanocarbon dispersion obtained by the dispersion treatment was adjusted to 20 ° C. using a B-type viscometer (No. 1 to 4 rotor) (trade name: B-type viscometer, model: BM, manufactured by Tokyo Keiki Seisakusho). The viscosity was measured by rotating at a rotation speed of 60 rpm for 1 minute, and the value was evaluated according to the following criteria A to D.
A: B type viscosity is 100 mPa · s or less, and the fluidity is very good.
B: B-type viscosity is 1000 mPa · s or less, and the fluidity is good.
C: B-type viscosity is 2000 mPa · s or less, and fluidity can be confirmed (practical lower limit).
D: B-type viscosity exceeds 5000 mPa · s and lacks fluidity (not practical).

From the results in Table 1, in Examples 1 to 7, carbon nanomaterial dispersions that were stably dispersed and had good fluidity were obtained. In Comparative Example 1, CNF was used instead of CNC, but both dispersibility and fluidity were poor. In Comparative Example 2 and Comparative Example 3, since CMC was used as the dispersant instead of CNC, the viscosity was high and the viscosity became viscous, and the dispersion equipment was clogged and the dispersion liquid could not be obtained. Since CNC was not used in Comparative Example 4, CNTs having high hydrophobicity alone could not be dispersed, resulting in large aggregates and sedimentation. In Comparative Example 5, since a surfactant was used instead of CNC as the dispersant, foaming occurred during the dispersion treatment and the treatment could not proceed.

(Preparation of dispersion liquid 1 to dispersion liquid 4)
Dispersion 1 corresponding to the dispersion of Example 6, dispersion 2 corresponding to the dispersion of Example 3, dispersion 3 corresponding to the dispersion of Example 1, and dispersion corresponding to the dispersion of Example 5. Liquid 4 was prepared respectively. The carbon nanotubes used in the preparation of the dispersion liquids 1 to 4 were CNT (A), and the dispersant was CNC.

(Making coated paper)
Paper with a pigment coating layer on high-quality paper that is a support ("Mucoat Neos" (registered trademark) manufactured by Hokuetsu Corporation, basis weight 157 g / m ² ) is prepared as a "paper base material" and dispersed. After the liquid 1 was coated on the paper with a bar coater, it was dried at 120 ° C. for 3 minutes to evaporate the water content, and a coated paper was prepared. That is, the "coated paper" is a paper base material provided with a coating layer containing CNT and CNC. For each of the dispersion liquid 2, the dispersion liquid 3, and the dispersion liquid 4, coated paper was prepared by the same operation as in the case of the dispersion liquid 1. Regarding the coating amount, the coating amount was adjusted so that the theoretical thickness of the coating layer of each coated paper was constant.

(Making a dry film)
The dispersion liquid 1, the dispersion liquid 2, the dispersion liquid 3 and the dispersion liquid 4 were each placed in a petri dish having a diameter of 8.5 cm and dried at 50 ° C. overnight to evaporate the water content, respectively, to prepare a dried film. That is, the "dry film" is a sheet containing CNT and CNC, and is not provided on a base material such as paper. After production, the film-forming property of each of the obtained dry films was observed. The specific evaluation criteria are as follows.
A: A solid substance having the shape and flexibility of a film, having no cracks, and containing nanocarbon and cellulose nanocrystals in a mutually mixed state was formed on the entire surface of the petri dish.
B: A solid substance having the shape and flexibility of a film and containing nanocarbon and cellulose nanocrystals in a mutually mixed state was formed on the entire surface of the petri dish, but cracks were generated in this solid substance. It was.
C: A solid substance having the shape and flexibility of the film, having no cracks, and containing nanocarbon and cellulose nanocrystals in a mutually mixed state was formed only in the black spot portion of the petri dish.

(Evaluation result of film formation property)
1a to 1d are images of the appearance of a dried film obtained by putting a carbon nanotube dispersion in a petri dish and drying it at 50 ° C. overnight. Table 2 shows the evaluation results of the film-forming property of the dried film.

As shown in FIGS. 1a to 1d and Table 2, the dispersion liquids 1 to 3 have better CNT dispersibility than the dispersion liquid 4, and therefore have good film forming properties.

No significant difference in film formation was confirmed between the dispersions 1 to 3, the shape and flexibility of the film were observed on the entire surface of the petri dish, there were no cracks, and nanocarbon and cellulose nanocrystals were mixed with each other. The solid matter contained in was formed. Since the content of CMC with respect to CNT was too low in the dispersion liquid 4, the shape and flexibility of the film were obtained only in the black spots of the petri dish, there were no cracks, and the nanocarbon and the cellulose nanocrystals were mutually exchanged. A solid containing in a mixed state was formed.

(Evaluation method of electromagnetic wave shielding property by coaxial tube method)
In the coaxial tube method, the electromagnetic wave shielding property was evaluated by measuring "S ₂₁ ". “S ₂₁ ” corresponds to transmission loss, and the larger the absolute value of “S ₂₁ ”, the higher the electromagnetic wave shielding property. As the testing machine, a network analyzer "ZVA67" manufactured by ROHDE & SCHWARZ and shield effect measurement kits "S-39D" and "GPC7" manufactured by KEYCOM were used. The measurement frequency was divided into 45 MHz to 3 GHz and 500 MHz to 18 GHz for measurement.

(Evaluation result of electromagnetic wave shielding property by coaxial tube method)
(1) Evaluation result when the ratio of CNT and CNC was changed The electromagnetic wave shielding property of the coated paper and the dried film produced as described above was evaluated. Table 2 shows the evaluation results of the electromagnetic wave shielding property of the coated paper. 2 and 3 are graphs showing the change of "S ₂₁ " of the coated paper with respect to the measurement frequency. The measurement frequency in FIG. 2 is 45 MHz to 3 GHz, and the measurement frequency in FIG. 3 is 500 MHz to 18 GHz. .. “S ₂₁ ” indicated as @ 300 MHz shown in Table 2 is obtained by extracting the value when the frequency is 300 MHz from FIG. “S ₂₁ ” shown in Table 2 as @ 7 GHz is obtained by extracting the value when the frequency is 7 GHz from FIG. FIG. 4 is a graph in which "S ₂₁ " is plotted against "mass ratio of CNT to total mass of CNT and CNC" shown in Table 2. The "mass ratio of CNT to the total mass of CNT and CNC" is the ratio (mass%) occupied by CNT when the total of the mass of CNT and the mass of CNC is 100% by mass.

Table 2 shows the thickness of the coating layer of the dispersion liquid. Here, the thickness of the coating layer of the dispersion liquid means the thickness of the coating layer obtained by drying the dispersion liquid. The thickness of the coating layer of the dispersion was measured by SEM analysis. Specifically, the thickness was obtained by subtracting the thickness of the paper base material (thickness of the woodfree paper and the thickness of the pigment coating layer) from the thickness of the entire coated paper.

As shown in Table 2 and FIGS. 2 to 4, the coated paper prepared from the dispersion liquids 1 to 3 has a frequency of both 300 MHz and 7 GHz as the mass ratio of CNT to the total mass of CNT and CNC increases. , The absolute value of "S ₂₁ " has increased. The coated paper prepared using the dispersion liquid 4 had a smaller absolute value of "S ₂₁ " at both frequencies of 300 MHz and 7 GHz than the coated paper prepared using the dispersion liquid 3. The absolute value of "S ₂₁ " of the coated paper produced using the dispersion liquid 4 is smaller than the absolute value of "S ₂₁ " of the coated paper produced using the dispersion liquid 3 as described above. As described above, the dispersibility of the dispersion liquid 4 is poorer than that of the dispersion liquid 3, and it is considered that the electromagnetic wave shielding property is lowered.

From the evaluation results of the coated paper prepared by using the dispersion liquids 1 to 4, the mass-based content ratio of CNT and CNC in the dispersion liquid was determined to be CNT: CNC = 1: 0.1 to 1: 5. It was found that the electromagnetic wave shielding property can be improved by preferably setting the ratio to 1: 1.

(2) Evaluation result when the thickness is changed Using the above-mentioned dispersion liquid 3 (mass-based content ratio of CNT and dispersant in the dispersion liquid 1: 1), the coating amount of the dispersion liquid 3 is changed. Each of the coated papers was prepared in the same manner as the above-mentioned preparation of the coated papers, except that the thickness of the coated layer of the dispersion liquid was changed. Further, a dry film was produced in the same manner as in the production of the dry film described above, except that the thickness of the dry film was changed by using the dispersion liquid 3 described above and changing the amount of the dispersion liquid 3 put into the petri dish. The thickness of the dry film was measured by SEM analysis in the same manner as the measurement of the thickness of the coating layer of the dispersion liquid. Then, the electromagnetic wave shielding property of the coated paper and the dried film was evaluated.

5 and 6 are graphs showing "S ₂₁ " for frequency. 7 and 8, there graph showing the "S _21" relative to the thickness, shown in FIG. 7, "S _21" is one in which the frequency is extracted the value at 300MHz from FIG. “S ₂₁ ” shown in FIG. 8 is obtained by extracting a value having a frequency of 7 GHz from FIG. In addition, in FIG. 5 and FIG. 6, each profile shown by the numerical value of 0.3 μm to 4.5 μm is the profile of the coated paper which has the coating layer of the dispersion liquid by the thickness, and is shown by the numerical value of 158 μm. The profile is a profile of a dry film having a thickness of 158 μm.

As shown in FIGS. 7 and 8, it was found that the larger the thickness, the higher the electromagnetic wave shielding property. As shown in FIGS. 7 and 8, especially at the measurement frequencies of 300 MHz and 7 GHz, the improvement of the electromagnetic wave shielding property becomes gradual from the thickness of 40 μm to 158 μm, so that the electromagnetic wave shielding property tends to be saturated at the thickness of 160 μm or more. I was able to predict that it was in. From this evaluation, it was predicted that the amount of CNTs could be reduced while keeping the transmission loss at -30 dB or less by setting the thickness to 40 μm or more and 160 μm or less.

(Evaluation method of electromagnetic wave absorption by microstrip line method)
The above evaluation of electromagnetic wave shielding property was performed by the coaxial tube method, but in this evaluation, the electromagnetic wave absorption property was evaluated by the microstrip line method using a near-field electromagnetic wave evaluation system compliant with IEC 62333. Similar to the preparation of the coated paper in "(2) Evaluation when the thickness is changed" described above, the dispersion liquid 3 is coated by changing the coating amount, and the thickness of the coating layer of the dispersion liquid is applied. (Thickness of the coating layer of the dispersion liquid 0.4 μm, 2.4 μm, 4.5 μm) were produced. Then, the electromagnetic wave absorption of the coated paper was evaluated. Further, as a reference example, the electromagnetic wave absorption of a paper base material (“Mucoat Neos” manufactured by Hokuetsu Corporation, basis weight 157 g / m ² ) and aluminum foil (thickness 6.5 μm) was evaluated.

As the testing machine, a network analyzer "ZVA67" manufactured by ROHDE & SCHWARZ and a test fixture "TF-18C" manufactured by KEYCOM were used. The measurement frequency was 500 MHz to 18 GHz.

(Evaluation result of electromagnetic wave absorption by microstrip line method)
FIG. 9 is a graph showing the evaluation results of electromagnetic wave absorption by the microstrip line method. The vertical axis “Rtp” in FIG. 9 indicates the transmission attenuation factor. The larger the absolute value of the transmission attenuation factor, the higher the electromagnetic wave absorption.

As shown in FIG. 9, it was found that the coated paper provided with the coating layer containing CNT and CNC has higher electromagnetic wave absorption than the paper base material and the aluminum foil. By this evaluation, it was possible to confirm the electromagnetic wave absorption of the coated paper containing CNT.

Claims (13)

1. A nanocarbon dispersion characterized by containing nanocarbon, cellulose nanocrystals, and a dispersion medium.
2. The nanocarbon dispersion according to claim 1, wherein the concentration of the nanocarbon is 1% by mass or more.
3. The nanocarbon according to claim 1 or 2, wherein the content ratio (nanocarbon: cellulose nanocrystal) based on the mass of the nanocarbon and the cellulose nanocrystal is 1: 0.1 to 1:10. Dispersion solution.
4. The claim is characterized in that the concentration of the nanocarbon is 1% by mass or more and 4% by mass or less, and the total concentration of the nanocarbon and the cellulose nanocrystal is more than 1% by mass and 15% by mass or less. The nanocarbon dispersion according to any one of 1 to 3.
5. The nanocarbon dispersion liquid according to any one of claims 1 to 4, wherein the dispersion medium is a polar solvent.
6. The nanocarbon dispersion according to claim 5, wherein the polar solvent is an alcohol, a ketone, an amide, water, or a mixture thereof.
7. A method for producing a nanocarbon dispersion, which comprises dispersing a mixture containing nanocarbon, cellulose nanocrystals, and a dispersion medium with a disperser.
8. The production of the nanocarbon dispersion according to claim 7, wherein the mixture is a mixture prepared by adding the cellulose nanocrystals to the dispersion medium, stirring the mixture, and then adding the nanocarbons. Method.
9. The method for producing a nanocarbon dispersion according to claim 7 or 8, wherein the cellulose nanocrystal is a spray-dried product.
10. The method for producing a nanocarbon dispersion liquid according to any one of claims 7 to 9, wherein the disperser is a homogenizer.
11. A nanocarbon dispersant characterized by containing cellulose nanocrystals.
12. An electromagnetic wave shielding material having a base material and a coating layer provided on the surface of the base material, and the coating layer contains nanocarbon and cellulose nanocrystals in a mutually mixed state.
13. An electromagnetic wave shielding material having the shape of a film and characterized in that the film contains nanocarbon and cellulose nanocrystals in a mutually mixed state.

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