WO2020100842A1 - Carbon nanotube granular material and method for producing same - Google Patents

Abstract

This carbon nanotube granular material is characterized by containing a synthetic water-soluble resin and carbon nanotubes, and by the amount of carbon nanotubes being 200-5000 parts by mass per 100 parts by mass of the synthetic water-soluble resin.

Description

Carbon nanotube granular material and method for producing the same

The present invention relates to a carbon nanotube granular material and a method for producing the same.

In recent years, carbon nanotubes (hereinafter sometimes referred to as CNTs) have attracted attention as a dream next-generation material and are used as antistatic agents or conductivity-imparting materials. Further, application development of CNTs is being promoted for use in tires, capacitors, conductive aids for lithium-ion batteries, or fiber-reinforced plastics.
The CNTs are carbon crystals having a diameter of several nm to about 200 nm, a length of about 0.1 μm to 2000 μm, a large aspect ratio, and a tubular structure. There are various types, and there are a single-wall carbon nanotube having a single-layer structure, a multi-wall carbon nanotube having a multi-layer structure, and a double-wall double-wall carbon nanotube which falls into the category of the multi-wall carbon nanotube. In addition, there are those in which both ends are blocked, those in which only one end is blocked, those in which both ends are open, and there are several types of rounding structures, such as the armature type.
The CNT manufacturing method includes an arc discharge type, a catalytic gas phase manufacturing method, a laser ablation method and other methods, but recently, the catalytic gas phase manufacturing method has become the mainstream.

It is generally known that CNTs are blended with various synthetic resins, rubbers and the like to impart electrical conductivity, high elasticity, high strength, thermal conductivity and the like. However, when using CNTs, there are concerns about safety, lack of dispersibility because the CNTs are tubular and are entangled with each other, and dispersability is poor, and handling is difficult. There is. For that reason, it has not been put to practical use despite being expected to be a "dream material."
Regarding the safety of CNTs, according to the opinion released by IARC (International Cancer Research Institute) in 2014, most CNTs are classified as "Group 3" (cannot be classified as carcinogenic), but even today, general users Among them, there is a strong recognition that "but CNT is a dangerous material." One of the reasons is that the shape of CNTs is fibrous like asbestos, the bulk density is very low at 1-5g / 100mL, and a large amount of air is entrained, resulting in a large scattering property. It is said that this is due to a large risk of inhalation to people.

Generally, an environmental risk is a possibility that a chemical substance or the like may adversely affect human health and growth and breeding of animals and plants via the environment. Conceptually, it is expressed as "risk = toxicity (toxicity) x exposure amount (intake amount)", and it can be said that a material is almost safe if there is no exposure even if it is obviously toxic. ..
Dust floating in the air, that is, dust that scatters, has a size, and in terms of health, there is a problem in how far the body can enter due to the size of the particles. Particles with a particle size larger than 10 to 20 μm fall early (called “falling dust”) and do not pose a problem. On the other hand, particles having a size of 10 μm or less easily reach the respiratory tract and lungs by respiration, and some of them enter the blood there, and some of them accumulate in alveoli and impair the function of the lungs. This is called inhalable (respirable) dust, and particles with an average particle size of 10 μm or less as an environmental standard have an average daily value of 0.10 mg / m ³ or less and an hourly value of 0.2 mg / m ³ or less. Has been defined.
The scattering property referred to in the present invention is premised on the scattering amount of inhalable dust mainly composed of particles of 10 μm or less.

As a reduced exposure product, it does not disperse in powder during packaging, transportation, inventory, or during actual use, and is easily dispersed in the dispersion process during kneading or molding of synthetic resin master batches and compounds. Is preferable.

As a carbon-based powder in which the final form of the product is spherical particles, there is carbon black (hereinafter sometimes referred to as CB) manufactured and sold at 12 million tons / year in the world. Since the bulk density of CB is much lower than that of CNT, it is generally low. Therefore, in general, using water as a binder, pan-type granulation method, drum-type granulation method, screw extrusion-type granulation method, stirring-type granulation method, or compression. Granulation is performed by a granulation method such as a molding granulation method. CB has a primary particle having a spherical shape and forms a structure in which particles are fused, and further, since functional groups such as oxygen and hydrogen are present on the surface of the particle, it has an affinity with water that functions as a binder. Yes, it is possible to granulate relatively easily. On the other hand, since CNTs have a developed crystal structure, few surface functional groups, and more air is entrained in the powder agglomerates than CB, the affinity for water is poor and granulation is not easy.
In order to solve this problem, methods for producing CNT granules as described in Patent Documents 1 to 7 have been proposed.

Japanese Patent Laid-Open No. 2005-239531 JP, 2006-143532, A International Publication No. 2017/033838 JP, 2009-062461, A International Publication No. 2009/008516 JP, 2010-043169, A Japanese Patent No. 4787892

However, the above conventional techniques have the following problems.
(1) In the technique disclosed in Patent Document 1 or Patent Document 2, a device is used that crushes powder in a high-speed air stream and further combines the powder. The original use of this device is to attach different kinds of fine powder particles to the surface of powder mother particles by impact with a high-speed air stream. Therefore, not only is it extremely difficult to granulate only one type of CNT, but even if it is possible, the particle diameter of the granulated product is very small, 200 μm or less, and it is difficult to granulate in the millimeter order. It is estimated that As described above, there are problems to be solved such as safety associated with scattering, environmental pollution, and handling.
(2) Further, even if it is an ordinary granulated product that does not use a binder, it is possible to improve the scattering property at the time of transportation or filling and the degree of environmental pollution as compared with the case where CNT powder is used. The workability of compounding, mixing and kneading with rubber, vehicle, etc. can be significantly improved. However, in order to satisfy the “preventive measures to prevent exposure to nanomaterials” that have become more and more severe these days, take one scattering property that considers the inhalable dust amount consisting of particles of 10 μm or less. Is not enough. Further, there is a problem that the initial compoundability or dispersibility at the time of compounding with a synthetic resin or the like is not satisfactory.

(3) Patent Document 3 is a CNT aggregate containing a rosin resin, which is a natural water-soluble resin. Since the rosin resin used is a natural product, it is a material whose production volume and price fluctuate greatly depending on the weather and labor problems in the production area. Therefore, in the paper manufacturing industry, which uses a lot of rosin resin as a sizing agent, the conversion to synthetic system (petroleum resin) with stable quality, price, and supply / demand is rapidly progressing. Further, as the effect of the invention, it is said that the wettability of CNTs is improved, the kneading is low, the scattering can be suppressed, and the dispersibility is excellent, but the data showing this effect is not described in Patent Document 3. Furthermore, the scattering property referred to in Patent Document 3 refers to all the dust particles scattered in the atmosphere, and is different from the inhalable dust amount consisting of particles of 10 μm or less, which is the object of the present invention. Further, since the granulated product of Patent Document 3 has a columnar shape, a bridge is likely to be formed in a hopper or the like when the granulated product is used, and the flow is bad.

(4) Patent Document 4 strongly disperses an aqueous resin and CNT with an ultrasonic disperser or a bead mill disperser to loosen CNT aggregates, coat the surface with the aqueous resin, and then further add a resin (heat Although it is a method of treating CNTs in which a plastic resin or a thermosetting resin is added and deposited, the content of CNTs in the aqueous resin is 10 mass% or less. The final shape is a paste, a dried solid (chip), or a crushed shape, and all the dried products are amorphous particles. When the irregular-shaped particles are filled with the irregular-shaped particles, not only the voids become large and the packing density becomes low, so that the packing amount in the packaging material decreases, but also the fluidity and the handling property in the hopper and the like are poor.

(5) Patent Documents 5 and 6 are polymer compositions obtained by mixing a single or a plurality of CNTs to prepare a granulated product having a predetermined particle diameter and a predetermined hardness, and dispersing this in a polymer. The basis of the granulated product production is (i) a method of infiltrating CNT powder into water to remove air, (ii) a granulating method by controlling the liquid-liquid interface and orienting the CNT at the interface (this method). Point is to use a plurality of solvents having different polarities.), Or (iii) a granulation method in which a plurality of CNTs having different sizes are geometrically entangled to form agglomerates. There are three manufacturing methods. However, all of these methods are significantly different from the granulation method of the present invention in that no resin is used as a binder. Further, in the specifications of Patent Documents 5 and 6, as a wet granulation method, a method in which a thermoplastic resin, a thermosetting resin, and a surfactant are used in combination with an organic solvent such as toluene or xylene is described. However, this is also a granulation method using a solvent, which is different from the granulation method in the present invention.

(6) In the technique disclosed in Patent Document 7, the inner or outer surface of CNTs is coated with a thermoplastic resin to improve the handling properties of CNTs, the dispersibility of the CNTs in a base resin, and the quantitative supply during kneading. And a method for producing a CNT granulated product having excellent features such as improved safety for the human body due to a significant reduction in airborne properties and improved scattering properties. However, it is necessary to use a large amount of solvent (about 10 times the amount of CNTs) during the production. For this reason, a hazardous material handling place and explosion-proof equipment required for the solvent removal or drying process are required, and the equipment investment becomes expensive. Further, since the solvent used is also expensive, as a result, it becomes a high-cost CNT granulated product, and there is a problem that the use is limited and it is difficult to spread. In addition, this method includes (i) a step of dispersing CNT powder in water, (ii) a step of dissolving a binder polymer in a solvent, (iii) a step of adding the CNT dispersed in water in the above (i) step to the above (ii) step. Granulating by adding the binder polymer solution obtained in step by step, (iv) draining the granules obtained in step (iii) above, (v) air-drying the drained granules or 50 ° C or less (Vii) vacuum drying the pre-dried granules, (vii) then sieving the granules and packaging. In addition, in this method, in addition to the above steps (i) to (vii), a wastewater treatment step is required, so that there are various steps, and the above (i) step, (iii) step, and ( v) Each step requires several hours to several tens of hours. Therefore, this method has a problem that it is lacking in productivity and energy saving and labor saving.

The present invention can be produced without using an organic solvent, has appropriate hardness and particle size, and has a high bulk density, and can reduce the amount of inhalable dust consisting of particles of 10 μm or less, and It is intended to provide a manufacturing method thereof.

The carbon nanotube granular material of the present invention contains a synthetic water-soluble resin and carbon nanotubes, and the blending amount of the carbon nanotubes is 200 parts by mass or more and 5000 parts by mass or more with respect to 100 parts by mass of the synthetic water-soluble resin. It is characterized by the following.

In the carbon nanotube granular material of the present invention, the synthetic water-soluble resin is preferably at least one selected from the group consisting of polyacrylamide, polyethylene oxide, polyvinyl alcohol, polyethyleneimine, and polyvinylpyrrolidone.
In the carbon nanotube granular material of the present invention, it is preferable that the carbon nanotube has a fiber diameter of 0.3 nm or more and 200 nm or less and the carbon nanotube has a fiber length of 0.1 μm or more and 2000 μm or less.
In the carbon nanotube granular material of the present invention, the amount of inhalable (respirable) dust composed of particles of 10 μm or less is preferably 0.2 mg / m ³ or less.
In the carbon nanotube granular material of the present invention, the particle diameter is preferably 0.25 mm or more and 4 mm or less, and the hardness of particles having a particle diameter of 1 mm is preferably 10 g or more and 25 g or less.
In the carbon nanotube granular material of the present invention, the carbon nanotube granular material is preferably spherical.

The first method for producing carbon nanotube granules according to the present invention comprises the steps of dissolving a synthetic water-soluble resin in water to prepare an aqueous resin binder solution, and adding 200 parts by mass or more and 5000 parts by mass or less of carbon nanotubes to 100 parts by weight. Part of the aqueous solution of the resin binder containing a part by weight of the synthetic water-soluble resin is added little by little, and granulated to obtain a granulated product, and the granulated product is dried to form carbon nanotube particles. And a step of obtaining a product.
The second method for producing carbon nanotube granules of the present invention comprises a step of dissolving a synthetic water-soluble resin in water to prepare an aqueous resin binder solution, and 200 parts by mass or more and 5000 parts by mass or less of carbon nanotubes. A step of adding the resin binder aqueous solution containing a mass part of the synthetic water-soluble resin little by little, and granulating to obtain a granulated product, and the granulation using a rolling granulator. The method is characterized by comprising a step of sizing the product to obtain a sized product, and a step of drying the sized product to obtain a carbon nanotube granular material.

According to the present invention, it is possible to produce without using an organic solvent, have appropriate hardness and particle size, have a high bulk density, and reduce the amount of inhalable dust composed of particles of 10 μm or less. An object and a manufacturing method thereof can be provided.

1 is a schematic diagram showing a reoccurring dust amount measuring device for measuring an inhalable dust amount consisting of particles of 10 μm or less. 3 is a photograph showing a dried granulated product in the process of producing the CNT granular product of Example 1. 3 is a photograph showing the CNT granules obtained in Example 1. 5 is a photograph showing the CNT granules obtained in Example 2. 5 is a photograph showing the CNT granules obtained in Comparative Example 1. It is a photograph showing a CNT granular material obtained in Comparative Example 2, and is a photograph taken from the side. It is a photograph showing a CNT granular material obtained in Comparative Example 2, and is a photograph of a cut surface.

Hereinafter, embodiments of the carbon nanotube granular material and the method for producing the same of the present invention will be described.
[Method for producing granular carbon nanotubes]
First, a method for manufacturing the carbon nanotube granular material of the present embodiment will be described.
The method for producing the carbon nanotube granules of the present embodiment includes a step of dissolving a synthetic water-soluble resin in water to prepare an aqueous resin binder solution (an aqueous solution preparation step), and 200 parts by mass or more and 5000 parts by mass or less of CNTs. , A step of adding a resin binder aqueous solution containing 100 parts by mass of a synthetic water-soluble resin while adding little by little, and granulating to obtain a granulated product (granulating step) and a rolling granulator A step of sizing the granulated product to obtain a sized product (sizing process), and a step of drying the sized product to obtain a carbon nanotube granular material (granular material producing step). Is a method characterized by.

(Aqueous solution preparation process)
In the aqueous solution preparation step, the synthetic water-soluble resin is dissolved in water to prepare an aqueous resin binder solution.
The synthetic water-soluble resin used in the present embodiment is not a natural resin but a resin obtained by chemical synthesis and a resin that is soluble in water. The synthetic water-soluble resin is preferably a resin obtained by a polymerization reaction. Examples of the polymerization reaction include chain polymerization, sequential polymerization, living polymerization and the like. The natural resin derived from plants is pine resin (rosin), lacquer, dammar, mastic, and the like. The natural resin derived from animals is shellac, gelatin, casein and the like.
Since the synthetic water-soluble resin is water-soluble, CNT can be granulated using an aqueous solution of the synthetic water-soluble resin without using an organic solvent. In addition, since the synthetic water-soluble resin has stable properties, it has appropriate hardness and particle size, high bulk density, and can reduce the amount of inhalable dust composed of particles of 10 μm or less. You can get things.
The SP value of the synthetic water-soluble resin is preferably 12 or more from the viewpoint of further reducing the inhalable dust amount of particles of 10 μm or less in the obtained CNT granules.
Examples of synthetic water-soluble resins include polyacrylamide (SP value 14.2), polyethylene oxide, polyvinyl alcohol (SP value 12.6), polyethyleneimine, and polyvinylpyrrolidone (SP value 12.8). Among these, polyvinylpyrrolidone is particularly preferable. These may be used alone or in combination of two or more.

Examples of water used in this embodiment include pure water and purified water.
The dilution rate of the synthetic water-soluble resin with water depends on the kind of the synthetic water-soluble resin, but is usually 0.1% by mass or more and 10% by mass or less, preferably 0.4% by mass or more and 5% by mass or more. It is not more than mass%. When the concentration (solid content) of the synthetic water-soluble resin diluted with water is 0.4% by mass or more and 5% by mass or less, the synthetic water-soluble resin easily penetrates and diffuses inside the CNT aggregate during the granulation process. As a result, a granulated product uniformly coated with the synthetic water-soluble resin is obtained. As the concentration becomes lower than 0.4% by mass, the adhesive force between the CNT particles tends to be weakened, and as the concentration becomes higher than 5% by mass, the aqueous resin permeates the inside of the CNT aggregate, It is not preferable because it tends to be difficult to diffuse. As the concentration of the synthetic water-soluble resin becomes lower than 0.1% by mass or becomes thicker than 10% by mass, these tendencies become stronger, which is not preferable.

For the ratio of preliminarily diluting the synthetic water-soluble resin with water, confirm the optimum amount of water required for granulation in a preliminary test, and make a low-concentration resin binder aqueous solution that completely dissolves the synthetic water-soluble resin with that amount of water. It is preferable to determine by. This resin binder aqueous solution is added to CNTs in a stirring state by a fixed amount by a metering pump or the like. For quantitative addition, if a nozzle capable of atomizing spray is used at the tip, a uniform granulated product can be easily obtained.
By adding the synthetic water-soluble resin in a concentration as low as possible, the aqueous resin is more likely to permeate into the voids of the CNT, and the entire coating of the CNT can be uniformly coated.
By adding a surfactant to the resin binder aqueous solution, the resin binder aqueous solution can easily penetrate into the CNT.

(Granulation process)
In the granulation step, the resin binder aqueous solution containing 100 parts by mass of the synthetic water-soluble resin is added little by little to 200 parts by mass or more and 5000 parts by mass or less of the CNT, and the mixture is granulated to form a granulated product. To get
The following effects can be obtained by adding the resin binder aqueous solution little by little with the compounding amount of CNT to the synthetic water-soluble resin being within the above range.
(1) A synthetic water-soluble resin can be efficiently permeated into the aggregate of CNTs to granulate a granulated product having an appropriate particle size and hardness.
(2) The hardness of dried CNT granules can be maintained at an appropriate level, powdering and scattering properties during handling can be reduced, and further, when used for resins, inks, paints, batteries, etc. The dispersibility can be made suitable.
Here, the blending amount of CNT is more preferably 300 parts by mass or more and 3000 parts by mass or less with respect to 100 parts by mass of the synthetic water-soluble resin (calculated as solid content). If it is less than 300 parts by mass, the granulated product tends to be hard and the dispersibility tends to be poor, and if it exceeds 3000 parts by mass, pulverization and scattering amount at the time of handling increase, which is not preferable in terms of safety. There is a tendency. Further, if the content of CNT is less than 200 parts by mass or more than 5000 parts by mass, these tendencies are remarkable, which is not preferable.

A spherical granulated product can be obtained by spray-adding an aqueous resin binder aqueous solution diluted with water little by little and in a mist state to the CNTs in a stirring state, while also considering the permeation rate into the CNTs. The granulation method is a method in which the aqueous resin is added little by little to the CNTs in a stirring state, and the granulation is performed by batch method or continuous method. In the case of the batch method, a low-concentration aqueous resin solution, which is weighed according to the particle size of the target substance, is sprayed in a fixed amount. In order to uniformly spray the liquid, it is desirable to use a spray nozzle of a fan type, an empty cone type, a full cone type or the like.
Incidentally, it was found that by adding an aqueous resin aqueous solution to the CNTs in a stopped state and then agitating and granulating, lumps and dumplings of the CNTs and the aqueous resin were formed, and the desired finely granulated product was not obtained. .. Furthermore, when only water was added to and mixed with CNTs in a stirring state, the water-soluble resin was added little by little in the form of powder, and the resin did not dissolve in water and adhered to the granulated product in the state of powder. It was in the form. In this state, there was almost no change even when dried.

The amount of water with respect to CNT in the granulation step is preferably 5 times or more and 8 times or less, more preferably 5.5 times or more and 7.5 times or less. When the water content is 5 times or less, there is a large amount of powdery CNTs, and it tends to be difficult to form a granulated product. Also, if the water content is 8 times or more, the granulated product will be considerably wetted, and if this is sized, it will become a large granulated product (pachinko balls (diameter 11 mm) or more) and spherical granules of 4 mm or less that are easy to handle. This is not preferable because it tends to be difficult to obtain a product.

In the CNT, a single-layer CNT in which one carbon film (graphene sheet) is wound in a cylindrical shape, a two-layer CNT in which two graphene sheets are concentrically wound, and a plurality of graphene sheets are concentrically wound. There are multi-layered CNTs. In the present embodiment, the single-layer CNT, the double-layer CNT, and the multi-layer CNT may be used alone or in combination of two or more.
The purity of CNT is preferably at least 80% or higher. During the production of CNT, fullerenes, graphite and amorphous carbon are simultaneously produced as by-products, and catalytic metals such as nickel, iron, cobalt and yttrium also remain. Purification is preferably carried out to remove these impurities. The purification method is not particularly limited, but examples thereof include oxidation treatment with sulfuric acid and nitric acid, halogen gas treatment, heat treatment at 2000 ° C. to 3000 ° C., and ultrasonic treatment. It is also preferable to perform separation and removal with a filter at the same time from the viewpoint of improving the purity.
The average fiber diameter and length of CNT are not particularly limited and can be appropriately selected according to the application. The fiber diameter is usually 0.3 nm or more and 200 nm or less, preferably 1 nm or more and 100 nm or less. The fiber length is usually 0.1 μm or more and 2000 μm, and preferably 1 μm or more and 1000 μm or less.
Regarding the fiber diameter, the minimum diameter considered to be producible by modern technology is about 0.3 nm, but it may be smaller than 0.3 nm. Also, as the fiber diameter becomes larger than 100 nm, the electrical and mechanical properties tend to deteriorate, and when it becomes larger than 200 nm, the superiority with CB, carbon nanofibers, etc. tends to disappear.
The fiber length is related to the conductivity, mechanical properties, dispersibility, etc., and as the fiber length becomes smaller than 1 μm, the conductivity and mechanical properties tend to be difficult to develop. Further, as the fiber length exceeds 1000 μm, the entanglement of the fibers becomes stronger, so that not only the number of poorly dispersed lumps increases but also the number of cut fibers during kneading and dispersion tends to be unfavorable. When the fiber length is smaller than 0.1 μm or exceeds 2000 μm, these tendencies are further increased, which is not preferable.

Wet granulation is used as the granulation method. Wet granulation includes rolling granulation, fluidized bed granulation, stirring granulation, compression granulation, extrusion granulation, crush granulation, and the like, based on the principle of the granulation method. In this embodiment, the stirring granulation method or the tumbling granulation method is preferable. This is because the apparatus can be easily made compact, the granulation time can be shortened, and the versatility is excellent.
The equipment used for stirring granulation can be roughly classified into a batch type and a continuous type, and as a representative of the batch type, a Henschel type stirring granulator or an intensive mixer, and as a continuous type, a twin screw is used for the production. A biaxial pin type granulator for granulating can be used.
As Henschel type, Hi-speed mixer series of Artechnica Co., Ltd., SPG series of Technopaudal Co., Ltd., FM mixer of Nippon Coke Industry Co., Ltd., SMB and SM series of Kawata Co., Ltd. or Paulex Co., Ltd. VG series and the like.
Examples of the intensive mixer include Maschinenfabrik Gustav Irish (Germany).
Also, as the twin-spin type, there is Dow Pelletizer of Shin-Nichinan Co., Ltd.
When manufacturing on a small scale, a food processor, a household mixer, or an ultra-small laboratory Henschel mixer is suitable.

As a method of continuous granulation, taking a pin granulator as an example, (1) CNT powder is quantitatively charged from a charging port into a device rotating at a stirring speed of 500 to 3000 rpm, preferably 1000 to 2000 rpm. , (2) An aqueous resin solution is added from an injection port in the latter stage of the injection port for granulation, (3) a granulated product is taken out from the ejection port, and dried in a drying step (4). Granulation performance is adjusted by the residence time in the granulator. The longer the residence time, the more spherical the granules can be obtained. In addition, a plurality of pin type granulators may be continuously installed in two stages or three stages.
On the other hand, in the case of the batch type, taking a Henschel type granulator as an example, after inserting a predetermined amount of CNT powder into the granulator, the mixture is stirred at 300 to 2500 rpm, preferably 500 to 2000 rpm, and the aqueous resin solution is added thereto. Granules are obtained by adding little by little as quantitatively as possible, observing when the desired particle size is reached, taking out and drying.
On the other hand, as the rolling granulator, there are a pan type granulator, a drum type granulator, a horizontal vibrating pan type granulator, a vibration stirring type granulator, a vibrating bed type granulator and the like. The most commonly used rolling granulators are the pan-type granulator and the drum-type granulator. Among them, the bread-type granulator is preferred because of its simple structure, easy operation, visible granulation state, and easy maintenance.

(Sizing process)
In the granule sizing step, the granulated product is granulated using a rolling granulator to obtain a granulated product.
As described above, by sizing the granulated product using the tumbling granulator, a spherical granulated product close to a true sphere can be obtained. The principle of the rolling granulation method for obtaining a granulated product from powder can be divided into the following three stages.
(1) A step in which several or several tens of primary particles are combined to form a nucleus (2) A step in which the particles collide with other particles or nuclei centering on the nucleus and become larger while adhering (3) Finally, the particle becomes larger The spherical particles are further rolled and subjected to frictional force and the gravity of the particles themselves, so that the inside becomes dense and the surface becomes smooth. However, in the case of CNT, most of the spaces between the particles are filled with air. Therefore, the bulk density is extremely low. For example, kumano kano nano 100P has a bulk density of 0.015 g / mL. In such a powder having an extremely low bulk density, particle nuclei are not formed even if the powder is rolled as it is. A common method is to add water to this to form a sticky film on the particle surface, and strengthen the contact and adhesion with surrounding particles to form nuclei for granulation. However, since CNTs have crystallites developed and the surface of the particles has few functional groups that are compatible with water, even if water is added, the water will not be repelled and the adhesive will not function. Therefore, the rolling granulation method using a pan type, a drum type, or the like as a container has not been utilized as a CNT granulating machine.
On the other hand, the present inventor transferred a granulated product (granulated product obtained in the granulation step) produced in advance with a wet stirring granulator with slightly less water than usual to a tumbling granulator, It was found that by doing so, spherical granules having a smooth surface can be obtained.
The water content of the granulated product in the granulation step is preferably 20% by mass or less, and more preferably 1% by mass or more and 10% by mass or less, based on 100% by mass of the granulated product.

(Particulate production process)
In the granule production step, the sized granules are dried to obtain CNT granules.
A vacuum dryer or a hot air dryer is used for drying. In the case of a granulated product containing a solvent, it is not possible to use a hot air dryer, but in the present embodiment, since a solvent is not used, a hot air dryer can be used.
As the hot air dryer, a vibration / fluid dryer, a fluid dryer, a box dryer, a dryer dryer or the like can be used. On the other hand, as the vacuum (decompression) dryer, a vacuum tray dryer, a vacuum outer mixer type dryer, a box type dryer, or the like can be used.
Since the drying temperature is preferably a temperature at which the resin used as the binder does not deteriorate, an optimum temperature or maximum temperature exists depending on the type of synthetic water-soluble resin. Generally, the drying temperature is 40 ° C or higher and 200 ° C or lower, preferably 50 ° C or higher and 150 ° C or lower, and more preferably 60 ° C or higher and 100 ° C or lower. Further, the drying time is usually 1 hour or more and 20 hours or less, preferably 2 hours or more and 10 hours or less, though it depends on the drying temperature.
A step of sieving the dried sized product with an ASTM sieve standard and 60 mesh (opening 0.25 mm) may be added.

[Particles of carbon nanotube]
Next, the carbon nanotube granular material of the present embodiment will be described.
The carbon nanotube granular material of the present embodiment contains a synthetic water-soluble resin and CNT, and the compounding amount of CNT is 200 parts by mass or more and 5000 parts by mass or less with respect to 100 parts by mass of the synthetic water-soluble resin. It is a thing. The carbon nanotube granular material is preferably spherical. By setting the amount of CNT to be mixed with the synthetic water-soluble resin within the above range, the same effect as that described in the granulation step in the method for producing carbon nanotube granules of the present embodiment described above can be obtained.
The CNT granules of this embodiment can be produced, for example, by the above-described method for producing carbon nanotube granules of this embodiment.
Further, the synthetic water-soluble resin and CNT are the same as those used in the method for producing the carbon nanotube granular material of the present embodiment described above.

In the CNT granular material of the present embodiment, the amount of inhalable (respirable) dust composed of particles of 10 μm or less is preferably 0.2 mg / m ³ or less. The inhalable dust amount is more preferably 0.1 mg / m ³ or less.
Under the Air Pollution Control Act, among particulate pollutants, inhalable dust that stops in the nose or throat, inhalable dust that reaches the trachea through the throat (Solasic) dust, and inhalation that reaches alveoli (respirable) I call it dust. Particularly, regarding the respirable dust amount of 10 μm or less, as an environmental standard, (i) the daily average of 1 hour value is 0.1 mg / m ³ or less, and (ii) 1 hour value is 0.2 mg / m ³ or less. Is defined as
The inhalable dust amount can be measured, for example, by the recurrent dust amount measuring device shown in FIG. The recurrent dust amount measuring apparatus 10 shown in FIG. 1 includes a sample feeding section 1, a connecting section 2, a multi-stage particle sizer 3, a filter paper holder 4 for different diameter adapters, a connecting tube 5, a flow meter 6, and a connection. The tube 7 and the pump 8 are provided. The sample loading unit 1 includes a double ball 11 and an impinger 12. The connection part 2 is provided with an outside air suction port 21. As the recurrent dust amount measuring device 10, for example, a sky-2 type manufactured by Shibata Scientific Co., Ltd. can be used. Then, in the measurement, CNT was introduced from the sample introduction unit 1 in the air flow of 10 L / min, and the amount of scattering was calculated by the mass adsorbed on the filter paper set at the device outlet (filter paper holder 4 for different diameter adapter). Also, in the measurement, the sample amount was changed to 5 levels, the amount of each scattering was calculated, and it was graphed, and the dust amount when the sample amount was 270 mg was adopted as the inhalable dust amount consisting of particles of 10 μm or less did.
When the inhalable dust amount is 0.2 mg / m ³ or less, the following effects can be obtained.
(1) Since the inhalability of particles of 10 μm or less is 0.2 mg / m ³ or less, preferably 0.1 mg / m ³ , the load on the working environment can be reduced and the safety can be significantly increased.
(2) The characteristic of the inhalable dust amount is related to the hardness of the granulated product, but it varies depending on the type of the binder, the amount of the adhering substance, or the granulation method even if the hardness is the same. Then, when wet granulation is performed using a synthetic water-soluble resin and then granulated by a rolling granulator, the amount of inhalable dust can be particularly reduced.

The particle diameter of the CNT granules of the present embodiment is preferably 0.25 mm or more (on ASTM 60 mesh) and 4 mm or less (on ASTM 5 mesh). Further, this particle diameter is more preferably 0.3 mm or more (on the ASTM 50 mesh) and 2.83 mm or less (on the ASTM 7 mesh). As the particle size becomes smaller than 0.3 mm, the fluidity from the hopper or the like decreases, automatic metering becomes difficult, and the amount of CNT particles scattered tends to increase in the use environment. Further, as the particle diameter becomes larger than 2.83 mm, it is difficult to make the granulated material into fine particles or crushed during kneading or dispersion with a synthetic resin or the like, which tends to cause poor dispersion, which is not preferable. In particular, when the particle size is smaller than 0.25 mm or the particle size is larger than 4 mm, this tendency is remarkable, which is not preferable.
The particle size of the CNT particles can be determined by placing the CNT particles together with a measure and observing the particles with an optical microscope. Further, generally, it is measured in accordance with JIS K6219-4 "How to obtain size distribution of granulated particles".

In the CNT granular material of the present embodiment, the hardness of particles having a particle diameter of 1 mm is preferably 10 g or more and 25 g or less.
When the hardness of the CNT granules exceeds 25 g, not only the initial dispersibility but also the final dispersibility tends to be deteriorated when compounding and dispersing in the synthetic resin, rubber, water, solvent, or vehicle. Further, as the hardness of the CNT granules becomes smaller than 10 g, powdering tends to occur at the time of packaging, transportation, stocking, compounding and kneading, and the like, which tends to cause environmental pollution, which is not preferable.
The hardness of the CNT granules can be measured according to the method for determining the hardness of granulated particles, JIS-K6219-3A method. There are manual and automatic measuring devices, and either one may be selected.

When the particle diameter is 0.25 mm or more and 4 mm or less, the shape is spherical, and the hardness of the particles having a particle diameter of 1 mm is 10 g or more and 25 g or less, the following effects can be obtained.
(1) The particle size of the CNT granules is 0.25 mm or more and 4 mm or less, 0.3 mm or more and 2.83 mm or less, and the hardness of the particles having a particle size of 1 mm is 10 g or more and 25 g or less. It is possible to prevent the formation of a bridge in the hopper or the like due to an object and to prevent the pipes from being blocked during idling.
(2) Since it has appropriate hardness and particle size and excellent fluidity, automatic weighing is possible. Therefore, unmanned operation is possible in the manufacturing process of the resin masterbatch or the resin compound, which is excellent in labor saving.
(3) It is possible to prevent the granules from scattering around when the device is maintained, and it is possible to significantly improve the safety.
(4) It is possible to significantly reduce powdering during transportation in a paper bag or a flexible container bag.

[How to use granular carbon nanotubes]
Next, a method of using the carbon nanotube granular material of the present embodiment will be described.
The CNT granules of this embodiment can be used by blending with various base resins, rubbers, vehicles, etc. and kneading. The composition obtained by kneading the CNT granules is used as various products, for example, a semiconductor tray, a transparent conductive film, or an antistatic molding or a conductive molding used for cars and the like.
Examples of the base resin include thermoplastic resins and thermosetting resins. Examples of the thermoplastic resin include polyolefin resins (polypropylene, polyethylene, etc.), polystyrene, rubber-modified impact-resistant polystyrene, ABS resin, PVC resin, polyamide resin, polyester resin, polyacetal resin, polycarbonate resin, and polysulfone resin. Is mentioned. Examples of thermosetting resins include unsaturated polyester resins, vinyl ester resins, epoxy resins, phenol resins, and polyimide resins.
Further, the CNT particles of the present embodiment can be dispersed in a vehicle such as water and a solvent and used as a conductive ink, a conductive paint, a capacitor, a conductive auxiliary agent for a lithium ion battery, or a material for a fuel cell. Furthermore, the CNT granules of the present embodiment can be compounded with rubbers such as SBR, BR, NR, IR, NBR, EPDM, urethane rubber, and silicone rubber, and applied to tires or various rubber products.

Since the CNT granules of this embodiment are used by kneading with the base resin or the like as described above, it is preferable that the initial dispersibility is excellent.
The initial dispersibility of the CNT particles is measured, for example, by the following method. That is, first, 99 g of polyethylene resin (manufactured by Nippon Polyethylene Co., Ltd., trade name “Novatech LF280H”) is put into a 6-inch two-roll roll set at a roll temperature of 130 ° C. and wound around the roll. From above, 1 g was added little by little, and after the total amount was added, kneading was performed for 10 minutes, and a sheet having a thickness of about 3 mm was taken out. A sample having a diameter of 3 mm is prepared from this sheet using a punching blade, and pressed for 5 minutes by a press machine heated to 160 ° C. to form a thin film through which light of a fluorescent lamp transmits. The dispersibility is evaluated by observing this thin film with an optical microscope. As the evaluation standard of the initial dispersibility, CNT powder having the best dispersibility (Kanos100P manufactured by KUMHO Co., Ltd.) is 10 points, and the worst example 1 is 1 point.
In addition, here, the initial dispersibility will be supplemented. Particles exist in an aggregated state, and the form of aggregation is formed by aggregated particles (aggregates) as hard aggregates of primary particles, soft aggregated particles (agglomerates), and soft aggregated particles (flocculates) with loose bonds. ing. The initial dispersibility referred to here is an evaluation of the process of crushing the entire flocculate and a part of the agglomerates, and in the case of CNT granules, crushing of the granulated particles and the two components that constitute this. This is an evaluation that examines the degree of disintegration (unraveling) of secondary aggregation.
The CNTs having poor initial dispersibility have poor final dispersibility when the resin is melted in a shaver shaver state when it is kneaded with a twin-screw kneader or the like and it is difficult to take a share, for example, when polyethylene resin or the like is used. Further, when used in water or a solvent system, this tendency appears remarkably, and it is an extremely important evaluation method in evaluating the dispersibility of a material used for kneading having a relatively small shear.

[Operation and effect of this embodiment]
According to this embodiment, the following operational effects can be achieved.
(1) CNT powder can be granulated using a synthetic water-soluble resin diluted with water as a binder to obtain CNT granules excellent in safety, fluidity, and handleability.
(2) A wet granulated product using a synthetic water-soluble resin as a binder is further sized by a tumbling granulator to make a granulated product close to a true sphere while adsorbing fine powder that has not been granulated. Therefore, the granules have a large compressive strength and the like, and the pulverization resistance can be increased.
(3) The amount of CNT particles scattered (the amount of inhalable dust composed of particles of 10 μm or less) can be 0.2 mg / m ³ or less, and the risk of environmental pollution can be extremely reduced. Furthermore, CNT granules having excellent initial dispersibility can be obtained. Reducing the amount of inhalable dust is related to the hardness of the granulated product, but even with the same hardness, after granulating with a low-concentration water-soluble resin liquid as a binder, additional granulation is added with a rolling granulator. This is probably the result of sizing. Regarding the initial dispersibility, when granulating with a tumbling granulator, the CNT agglomerates are not in the form of hard amorphous dumplings, but granules with a shape like thin onions stuck together like an onion. I think it is because it was formed. The operation and effect of the present embodiment are as described above. On the other hand, the columnar granulated product has two surfaces, a hard body portion (body surface) and a relatively soft and brittle cut surface (side surface), If the cut surface is hardened to reduce the scattering property, the body surface becomes significantly harder and the granulated product has poor dispersibility. In addition, since it has a trade-off relationship such as a granulated product having a large scattering property when it is moved in the direction of improving the dispersion property, it is difficult to satisfy both the dispersion property and the scattering property.
(4) Since no solvent or oil is used in the manufacturing process, the cost is low and the manufacturing place is not limited. Further, the influence on the human body is reduced. More specifically, in terms of "equipment", (i) no expensive solvent is required, (ii) the process is simple, (iii) an expensive vacuum dryer is unnecessary compared to the hot air dryer, (iv) solvent It has the advantages of not requiring recovery equipment, (v) no deodorizing device, (vi) no local exhaust equipment, and (vii) no equipment with explosion-proof function. In addition, the “Industrial Accident Law and Fire Defense Law” (i) reduces the risk of fire, (ii) does not require a licensed person to handle dangerous materials (work chief), (iii) does not require various protective equipment, ( iv) No need to measure work environment every 6 months, (v) No special health check, (vi) Reduced hazard to human body, and (vii) Special hazardous materials for storing pre-dried products, solvents, etc. It has the advantage that no storage space is required. In this way, simplification is achieved in many aspects, and energy and labor can be saved.
(5) Compared with the techniques described in Patent Documents 5, 6 and 7, the amount of manufacturing equipment investment is greatly reduced, resource saving and labor saving are excellent, and CNT granulation is performed at a cost close to that of CB granulation. Can produce granules.

[Modification of Embodiment]
The present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within the scope of achieving the object of the present invention are included in the present invention.
For example, in the above-described embodiment, the true sphere is formed by two steps of a granulation step of obtaining a granulated product and a granulation step of granulating the granulated product obtained in the granulation step to obtain a granulated product. Although a spherical granulated product close to the above was produced, the present invention is not limited to this. For example, if it is possible to find a method capable of producing a spherical granulated product close to a true sphere by only a single granulating process of obtaining a granulated product, the sizing process can be omitted. An intensive mixer is preferable to a Henschel-type stirring granulator as a granulator that approaches a true sphere by a single granulation step.

Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The mixing ratios in the text are based on mass.

[Example 1]
In a 2 L SUS container, 480 g of ion-exchanged water heated to about 50 ° C. and a synthetic water-soluble resin (polyvinylpyrrolidone (PVP), “Pittscor K-30” manufactured by Daiichi Kogyo Co., Ltd., solid content 95%) As described above, 9.35 g (number-average molecular weight of 10,000) (8.89 g in terms of solid content) was charged and stirred for 5 minutes with a homomixer to completely dissolve the resin and prepare a resin binder aqueous solution. Then, 80 g (“K-Nanos 100P” manufactured by Kumho Co., Ltd.) as CNT powder was charged into a Henschel mixer “FM10C” (volume 9 L, processing capacity 6 L) manufactured by Nippon Coke Industry Co., Ltd., while stirring at 1000 rpm. From above, 489.4 g of the above resin binder aqueous solution was sprayed over 5 minutes. The liquid was sprayed using a diaphragm type metering pump (50 to 500 mL / min) manufactured by Meito Kakoki Co., Ltd. at a speed of 96 mL / min. Further, the spraying was performed in a fine mist state by attaching an empty cone nozzle KB (spraying flow rate of 2 to 107 L / hour) manufactured by Ikeuchi Co., Ltd. to the tip of the hose from the metering pump. The amount of water in this granulation is 6.0 times the amount of CNT. The resin amount with respect to CNT is 10.0% (the compounding amount of CNT is 900 parts by mass with respect to 100 parts by mass of resin).
After the total amount of the resin binder aqueous solution was added, the rotation speed of the Henschel mixer was lowered to the minimum and the mixture was further stirred for 2 minutes to obtain a wet granulated product (water content 85.7%). The temperature inside the Henschel mixer after the granulation was about 70 ° C., and almost no granules were attached to the wall of the mixer. This may be related to the use of hot water at 50 ° C. A part of the wet granulated product was dried with a hot air dryer at 90 ° C. until the water content was 1% or less, and a photograph thereof was taken. This photograph is shown in FIG.
Next, this wet granulated product was transferred to a pan-type granulator for granulation and sizing. The pan-type granulator uses a 500 mm diameter type manufactured by Mitsufuku Industry Co., Ltd., and while rotating at 10 to 45 rpm, the wet granulated product is gradually added over a period of about 10 minutes to make sure that the shape of the granule is true. When it became a ball, it was stopped to obtain a sized product. Then, it was dried with a hot air dryer at 90 ° C. until the water content became 1% or less, to obtain CNT granules. A photograph of the obtained CNT granules was taken. This photograph is shown in FIG.

[Example 2]
The wet granulated product obtained in the same manner as in Example 1 was dried with a hot air dryer at 90 ° C. until the water content was 10% or less, transferred to a pan-type granulator, and granulated and sized. .. The pan-type granulator uses a 500 mm diameter type manufactured by Mitsufuku Industry Co., Ltd., puts the entire amount of the wet granulated product while rotating at 40 rpm, and stops when the shape of the particle becomes a sphere, A sized product was obtained. Then, it was dried with a hot air dryer at 90 ° C. until the water content became 1% or less, to obtain CNT granules. A photograph of the obtained CNT granules was taken. This photograph is shown in FIG.

[Example 3]
The amount of ion-exchanged water in the resin binder aqueous solution was changed to 560 g, and the amount of polyvinylpyrrolidone was changed to 4.43 g (4.21 g in terms of solid content, and the amount of resin relative to CNT was 5.0%). CNT granules were obtained in the same manner as in Example 2 except for the above. The amount of water in this granulation is 7 times the amount of CNT, and the amount of water in the obtained wet granulated product is 87.5%.

[Example 4]
The amount of ion-exchanged water in the aqueous resin binder solution was changed to 560 g, and the amount of polyvinylpyrrolidone was changed to 2.60 g (2.47 g in terms of solid content, and the amount of resin relative to CNT was 3.0%). CNT granules were obtained in the same manner as in Example 2 except for the above. The amount of water in this granulation is 7 times the amount of CNT, and the amount of water in the obtained wet granulated product is 87.5%.

[Example 5]
Instead of polyvinylpyrrolidone, polyethyleneimine (PEI, "SP-018" manufactured by Nippon Shokubai Co., Ltd., molecular weight 1800, solid content of 98% or more) 9.07 g (solid content converted to 8.89 g, resin for CNT) CNT granules were obtained in the same manner as in Example 2, except that the amount was 10.0%. The amount of water in this granulation is 6 times the amount of CNTs, and the amount of water in the obtained wet granulated product is 85.7%.

[Example 6]
CNT granules were obtained in the same manner as in Example 1 except that an intensive mixer (Maschinenfabrik Gustaf Irish Co., Ltd.) was used as an apparatus used for stirring granulation instead of the Henschel mixer. The amount of water in this granulation is 6.1 times the amount of CNT.

[Comparative Example 1]
197 g of toluene heated to about 70 ° C. and 5.56 g of High Wax 320P (manufactured by Mitsui Chemicals), which is a low molecular weight thermoplastic resin as a binder resin, are added, and the resin is completely dissolved with stirring to form a resin binder. An aqueous solution was prepared. Next, 50 g of the same CNT powder as that used in Example 1 was put into a 10 L stainless steel round container, 4950 g of pure water was put therein, and then the mixture was stirred at about 6000 rpm for 30 minutes using a homogenizer stirrer. The amount of resin with respect to CNT is 10.0%. Next, the blade of the stirrer was changed to a screw type, and while stirring at about 1000 rpm, the whole amount of the resin binder solution was dropped little by little, and then 276 g of toluene was added while observing the granulation property. After removing water from the obtained granules with a 60 mesh sieve (filtered water was collected and treated at a wastewater treatment plant), it was air-dried in a draft for 10 hours, and then dried in a vacuum dryer set at 70 ° C for 8 hours. Then, water and toluene were completely removed (water content was 1% or less) to obtain CNT particles. The obtained CNT granules were spherical and the particle size was 0.5 to 3 mm. A photograph of the obtained CNT granules was taken. This photograph is shown in FIG.

[Comparative example 2]
A wet type wet process was performed in the same manner as in Example 3 except that a water-soluble rosin-based resin (natural resin rosin added with ethylene oxide, “REO-30” manufactured by Harima Kasei Co., Ltd.) was used instead of polyvinylpyrrolidone. A granulated product was obtained. The compounding amount of REO-30 with respect to 80 g of CNT powder was 4.2 g in terms of solid content (the amount of resin with respect to CNT was 5%).
Next, a multi-gran MG-55-2 manufactured by DALTON was used to obtain a cylindrical granulated product having a diameter of 4 mm. Then, it was dried with a hot air dryer at 90 ° C. until the water content became 1% or less, to obtain CNT granules. A photograph of the obtained CNT granules was taken. This photograph is shown in FIG. FIG. 6 (A) is a photograph taken from the side, and FIG. 6 (B) is a photograph taken of a cut surface.

[Reference Example A]
80 g of CNT powder ("K-Nanos 100P" manufactured by Kumho) was added to a HENSCHEL MIXER "FM10C" (volume: 9 L, processing capacity: 6 L) manufactured by Nippon Coke Industry Co., Ltd., and the mixture was stirred at 1000 rpm from the top. Ion-exchanged water (480 g) was sprayed over 5 minutes. The liquid was sprayed using a diaphragm type metering pump (50 to 500 mL / min) manufactured by Meito Kakoki Co., Ltd. at a speed of 96 mL / min. Further, the spraying was performed in a fine mist state by attaching an empty cone nozzle KB (spraying flow rate of 2 to 107 L / hour) manufactured by Ikeuchi Co., Ltd. to the tip of the hose from the metering pump. In addition, 9.35 g of synthetic water-soluble resin (polyvinylpyrrolidone (PVP), “Pitscol K-30” manufactured by Daiichi Kogyo Co., Ltd., solid content 95% or more, number average molecular weight 10000) (8.89 g in terms of solid content) ) Was added in four times. The amount of water in this granulation is 6.0 times the amount of CNT. The resin amount with respect to CNT is 10.0% (the compounding amount of CNT is 900 parts by mass with respect to 100 parts by mass of resin).
After the ion-exchanged water and the resin were all added, the rotation speed of the Henschel mixer was lowered to the minimum and the mixture was further stirred for 2 minutes to obtain a wet granulated product. The temperature inside the Henschel mixer after granulation was about 30 ° C.
Next, this wet granulated product was transferred to a pan-type granulator for granulation and sizing. The pan-type granulator uses a 500 mm diameter type manufactured by Mitsufuku Industry Co., Ltd., and while rotating at 10 to 45 rpm, the wet granulated product is gradually added over a period of about 10 minutes to make sure that the shape of the granule is true. When it became a ball, it was stopped to obtain a sized product. Then, it was dried with a hot air dryer at 90 ° C. until the water content became 1% or less, to obtain CNT granules.

[Evaluation of CNT granules]
The CNT granules were evaluated (bulk density, grain hardness, initial dispersibility, and inhalable dust content) by the following methods. The results obtained are shown in Table 1.
In addition, "K-Nanos 100P" manufactured by Kumho was evaluated as Reference Example 1, and "K-Nanos 100T" manufactured by Kumho was evaluated as Reference Example 2. The results obtained are shown in Table 1.
(1) Bulk Density The bulk density was measured according to JIS-K6219-2 method.
(2) Grain Hardness The grain hardness was measured according to JIS-K6219-3A method, Part 3 of the characteristics of CB granulated particles for rubber: Determination of hardness of granulated particles.
(3) Initial dispersibility 99 g of polyethylene resin (manufactured by Nippon Polyethylene Co., Ltd., trade name "Novatech LF280H") was put into a 6-inch two-roll roll set to a roll temperature of 130 ° C. and wound around the roll. From above, 1 g was added little by little, and after the total amount was added, kneading was performed for 10 minutes, and a sheet having a thickness of about 3 mm was taken out. A sample having a diameter of 3 mm was prepared from this sheet using a punching blade, and pressed for 5 minutes with a press machine heated to 160 ° C. to form a thin film through which light from a fluorescent lamp transmits. The dispersibility was evaluated by observing this thin film with an optical microscope. As the evaluation criteria of the initial dispersibility, the CNT powder (Knanos 100P manufactured by KUMHO) having the best dispersibility was 10 points, and the worst was Comparative Example 1 as 1 point.
(4) Inhalable dust amount As a recurrent dust amount measuring device, a sky-2 type manufactured by Shibata Scientific Co., Ltd. was used (see FIG. 1). Then, in the measurement, CNT granules were charged from the sample charging part in an air stream of 10 L / min, and the amount of scattering was calculated by the mass adsorbed on the filter paper set at the apparatus outlet. Also, in the measurement, the sample amount was changed to 5 levels, the amount of each scattering was calculated, and it was graphed, and the dust amount when the sample amount was 270 mg was adopted as the inhalable dust amount consisting of particles of 10 μm or less from the graph. did. Moreover, the numerical value compared with the result of the reference example 1 which is a CNT powder is also shown together.

From the results shown in Table 1, the CNT granules of Examples 1 to 6 of the present invention have a particle diameter of 1 mm, a hardness of 10 g or more and 25 g or less, and a bulk density of CNT powder as a raw material (Reference Example 1). It was found to have 7 to 9.3 times.
Further, it was found that the initial dispersibility of the CNT granules of the present invention was slightly lower than that of Comparative Example 1 and Comparative Example 2, although the initial dispersibility of the CNT granules slightly decreased as the hardness of the particles increased. Furthermore, the inhalable dust amount (respirable) of the CNT granules of the present invention composed of particles having a size of 10 μm or less is significantly lower than that of the raw CNT powder (Reference Example 1), and each is 0.1 mg / m ³ It turned out to be:
On the other hand, the CNT granules obtained in Comparative Example 1 were obtained by granulating using a solution of low molecular weight polyethylene dissolved in toluene instead of the synthetic water-soluble resin. The CNT granules are very hard. Therefore, the amount of inhalable dust consisting of particles of 10 μm or less is excellent, but the initial dispersibility is extremely poor. Further, although not shown in Table 1, there is a drawback that a hazardous material handling office, a dangerous material handling supervisor, explosion-proof equipment, wastewater treatment equipment and the like are essential for manufacturing.
Comparative Example 2 is a CNT granule containing 5% of a water-soluble rosin resin, but the granule is harder and has an initial dispersibility as compared with the CNT granule of Example 3 containing 5% of polyvinylpyrrolidone. Inferiority, and a large amount of inhalable dust composed of particles of 10 μm or less. In order to verify the cause, the micrographs of the CNT granules obtained in Comparative Example 2 (see FIGS. 6A and 6B) were observed. From FIG. 6A, it was found that the side surface of the columnar CNT granule was glossy and had few cracks and the like, and it was a granulated product that was nearly ideal as an extrusion granulated product. It is considered that the formation of such CNT granules may be due to the fact that the rosin resin has higher tackiness (resistance to tearing) and adhesive force than the synthetic resin. On the other hand, it is considered that the reason why the particles are hard and the initial dispersibility is poor may be related to the tack performance and the adhesive force.
Further, as the reason why the amount of inhalable dust composed of particles of 10 μm or less is inferior, as can be seen from FIG. 6B, a large amount of powdery CNTs are present on the cut surface of the cylindrical CNT granules, which scatters. Therefore, it is considered that the amount of inhalable dust composed of particles of 10 μm or less is increased.

The CNT granules of the present invention have appropriate hardness, have good scattering properties, and are particles having a respirable dust content of 10 μm or less which adversely affects human health. Further, by using the method for producing CNT granules of the present invention, a complicated precipitation step is not required, and a solvent that is a dangerous substance is not used, and the CNTs of the present invention are simpler than conventional ones. Granules can be produced. Therefore, the risk of causing health damage is low, and the CNT granules of the present invention can be produced at a significantly lower cost as compared with the prior art.
Furthermore, since the CNT granules of the present invention have an appropriate hardness, when manufacturing a resin composition using a base resin such as a thermoplastic resin, the CNT granules can be supplied in a fixed amount and continuously. It is possible to obtain a resin composition in a uniform mixed state.

Claims (8)

1. Contains synthetic water-soluble resin and carbon nanotubes,
   The carbon nanotube granular material, wherein the blending amount of the carbon nanotubes is 200 parts by mass or more and 5000 parts by mass or less based on 100 parts by mass of the synthetic water-soluble resin.
2. The carbon nanotube granular material according to claim 1, wherein
   The carbon nanotube particulate material, wherein the synthetic water-soluble resin is at least one selected from the group consisting of polyacrylamide, polyethylene oxide, polyvinyl alcohol, polyethyleneimine, and polyvinylpyrrolidone.
3. The carbon nanotube granular material according to claim 1 or 2,
   The fiber diameter of the carbon nanotubes is 0.3 nm or more and 200 nm or less,
   The carbon nanotube granular material, wherein the fiber length of the carbon nanotube is 0.1 μm or more and 2000 μm or less.
4. The carbon nanotube granular material according to any one of claims 1 to 3,
   An inhalable (respirable) dust amount of particles of 10 μm or less is 0.2 mg / m ³ or less.
5. The carbon nanotube granular material according to any one of claims 1 to 4,
   The particle size is 0.25 mm or more and 4 mm or less,
   Particles having a particle size of 1 mm have a hardness of 10 g or more and 25 g or less.
6. The carbon nanotube granular material according to any one of claims 1 to 5,
   The carbon nanotube granules are spherical in shape.
7. Dissolving a synthetic water-soluble resin in water to prepare a resin binder aqueous solution,
   A step of adding 200 parts by mass or more and 5000 parts by mass or less of carbon nanotubes while adding the resin binder aqueous solution containing 100 parts by mass of the synthetic water-soluble resin little by little, and granulating to obtain a granulated product. When,
   A step of drying the granulated product to obtain carbon nanotube granules.
8. Dissolving a synthetic water-soluble resin in water to prepare a resin binder aqueous solution,
   A step of adding 200 parts by mass or more and 5000 parts by mass or less of carbon nanotubes while adding the resin binder aqueous solution containing 100 parts by mass of the synthetic water-soluble resin little by little, and granulating to obtain a granulated product. When,
   A step of sizing the granulated product using a rolling granulator to obtain a sized product,
   And a step of obtaining the carbon nanotube particles by drying the sized product.

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