Carbon nanotube dispersion and preparation method thereof

Abstract

The present invention relates to a carbon nanotube dispersion and a method for preparing the same, wherein the carbon nanotube dispersion comprises: carbon nanotubes; a first dispersant, the first dispersant being a carboxyalkyl cellulose having a weight average molecular weight of 9,000 g / mol or less; a second dispersing agent, wherein the second dispersing agent is polyvinyl butyral (PVB); and a solvent, and the carbon nanotube dispersion of the present invention has a low initial viscosity and a low viscosity change rate, and thus is excellent in storage stability and processability.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0044854 filed on April 5, 2023, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to a carbon nanotube dispersion and a method for preparing the same, wherein the carbon nanotube dispersion itself has a low initial viscosity and a small change in viscosity over time, and therefore has excellent storage stability, and has excellent processability when a coating process is performed. Background Art

[0005] Carbon nanotubes are macromolecules in which a hexagonal honeycomb graphite surface in which one carbon atom is bonded to three other carbon atoms is wound into a nanometer-sized diameter. Carbon nanotubes are hollow and therefore lightweight, and have electrical conductivity as good as that of copper, thermal conductivity as excellent as that of diamond, and tensile strength as good as that of steel. According to their winding shape, carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT) and rope-shaped carbon nanotubes (Rope Carbon Nanotube).

[0006] Due to its excellent conductivity, carbon nanotubes have been widely used as conductive materials for secondary batteries in recent years, but carbon-based conductive materials including carbon nanotubes have the problem of being easily aggregated and unable to be uniformly dispersed in the electrode slurry composition. If the conductive material aggregates in the electrode slurry composition, the conductive material is not uniformly distributed in the active material layer during the process of forming the electrode, which also leads to a decrease in the performance of the secondary battery. Therefore, research on various technologies is being conducted to ensure that the conductive material is uniformly dispersed in the electrode slurry composition.

[0007] Representationally, the attempt to increase dispersibility by introducing conductive material and dispersant simultaneously is the most common.Specifically, the method for improving the dispersibility under the dispersed state by introducing a cellulose-based dispersant or a polymer component such as hydrogenated nitrile butadiene rubber (HNBR) as a dispersant.Specifically, if a cellulose-based dispersant known as a typical carbon nanotube dispersion is used as a unique dispersant, there is an effect that the rate of change of viscosity over time is reduced, but there is a problem that the initial viscosity of the dispersion itself is high, and if polyvinyl butyral (PVB) is used as a unique dispersant, there is an effect that reduces the initial viscosity of the dispersion itself, but there is a problem that the rate of change of viscosity over time is too high.In addition, if a cellulose-based dispersant and a typical polymer-based dispersant such as hydrogenated nitrile butadiene rubber (HNBR) are used simultaneously, there is not only an increase in initial viscosity, and a problem that the rate of change of viscosity over time also increases.

[0008] Therefore, there is a need to develop a new carbon nanotube dispersion having a low initial viscosity and minimized viscosity change over time, thereby being able to maintain the viscosity and viscosity stability at excellent levels.

[0009] Prior art literature

[0010] (Patent Document 1) KR 10-2022-0003984A Summary of the invention

[0011] Technical issues

[0012] An object of the present invention is to provide a carbon nanotube dispersion and a method for preparing the same, wherein the dispersion itself has a low initial viscosity so that workability is excellent when a coating process is performed and storage stability is excellent due to a small change in viscosity over time.

[0013] Technical Solution

[0014] In order to achieve the above object, the present invention provides a carbon nanotube dispersion and a preparation method thereof.

[0015] Specifically, (1) the present invention provides a carbon nanotube dispersion comprising: carbon nanotubes, a first dispersant, a second dispersant and a solvent, wherein the first dispersant is a carboxyalkyl cellulose having a weight average molecular weight of 9,000 g / mol or less, the second dispersant is polyvinyl butyral (PVB), and the weight ratio between the first dispersant and the second dispersant is 1:2.5 to 1:10.

[0016] (2) In the above (1), the present invention provides a carbon nanotube dispersion, wherein the combined content of the first dispersant and the second dispersant is 50 to 700 parts by weight based on 100 parts by weight of the carbon nanotubes.

[0017] (3) In any one of (1) and (2) above, the present invention provides a carbon nanotube dispersion, wherein the content of the first dispersant is 0.1 wt % to 5 wt % based on the total dispersion weight.

[0018] (4) In any one of (1) to (3) above, the present invention provides a carbon nanotube dispersion, wherein the content of the second dispersant is 0.1 wt % to 5 wt % based on the total dispersion weight.

[0019] (5) In any one of (1) to (4) above, the present invention provides a carbon nanotube dispersion wherein the content of the carbon nanotubes is 5% by weight or less based on the total dispersion weight.

[0020] (6) In any one of (1) to (5) above, the present invention provides a carbon nanotube dispersion, wherein the first dispersant is carboxymethyl cellulose (CMC) or carboxyethyl cellulose (CEC).

[0021] (7) In any one of (1) to (6) above, the present invention provides a carbon nanotube dispersion, wherein the average molecular weight of the first dispersant is 2,000 g / mol to 8,000 g / mol.

[0022] (8) In any one of (1) to (7) above, the present invention provides a carbon nanotube dispersion wherein the second dispersant has a unit content of vinyl alcohol of 10% by weight to 22% by weight in polyvinyl butyral.

[0023] (9) In any one of (1) to (8) above, the present invention provides a carbon nanotube dispersion, wherein the average molecular weight of the second dispersant is 20,000 g / mol or less.

[0024] (10) The present invention provides a method for preparing a carbon nanotube dispersion according to any one of (1) to (9), the method comprising (S10) mixing carbon nanotubes, a first dispersant, a second dispersant, and a solvent, and (S20) dispersing the mixture.

[0025] (11) In the above (10), the present invention provides a method for preparing a carbon nanotube dispersion, wherein the above step S20 includes (S21) stirring at a rate of 5,000 rpm to 10,000 rpm for 30 minutes or more.

[0026] Beneficial Effects

[0027] The carbon nanotube dispersion of the present invention has a low initial viscosity of the dispersion itself, and thus has excellent workability when a coating process is performed, and also has a small change in viscosity over time, and thus has excellent storage stability. DETAILED DESCRIPTION

[0028] Hereinafter, the present invention will be described in more detail.

[0029] It will be understood that the terms or words used in the specification and claims should not be interpreted as limited to having the meanings defined in commonly used dictionaries, but should be interpreted as having meanings and concepts consistent with the technical ideas of the present invention based on the concept that the inventor can appropriately define the terms to best explain the principle of the present invention.

[0030] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of the present invention. Terms in the singular may include plural forms unless the context clearly indicates otherwise.

[0031] In this specification, it should be understood that the terms "include", "comprises" or "has" are intended to specify the presence of stated features, quantities, steps, elements, or a combination thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or a combination thereof.

[0032] In the present specification, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the nitrogen adsorption amount at liquid nitrogen temperature (77K) using Belsorp-mino II of BEL Japan Co.

[0033] In this specification, "the length of the carbon nanotube" can be measured using an atomic force microscope or a scanning electron microscope.

[0034] Carbon Nanotube Dispersion

[0035] The present invention provides a carbon nanotube dispersion, which comprises: carbon nanotubes, a first dispersant, a second dispersant and a solvent, wherein the first dispersant is a carboxyalkyl cellulose having a weight average molecular weight of 9,000 g / mol or less, the second dispersant is polyvinyl butyral (PVB), and the weight ratio between the first dispersant and the second dispersant is 1:2.5 to 1:10.

[0036] As described above, if a cellulose-based dispersant known as a typical dispersant for carbon nanotube dispersion is used as the only dispersant, there is an effect of reducing the rate of change of viscosity over time, but there is a problem of high initial viscosity of the dispersion itself. In order to make up for the above-mentioned shortcomings, in addition to the cellulose-based dispersant, a typical polymer-based dispersant such as hydrogenated nitrile rubber (HNBR) is also applied separately, but there is a problem that not only the initial viscosity increases, but also the rate of change of viscosity over time increases. Therefore, the inventors of the present invention have studied a dispersant that can maintain the technical advantages of a typical cellulose-based dispersant while overcoming the shortcomings of a cellulose-based dispersant with a high initial viscosity, and as a result, it was determined that if polyvinyl butyral (PVB) is applied together with a carboxyalkyl cellulose having a specific weight-average molecular weight of 9,000 g / mol or less, both the initial viscosity and the rate of change of viscosity over time can be reduced, and the present invention has been completed.

[0037] In particular, it has been determined that in the present invention, the weight ratio between the first dispersant, which is carboxyalkyl cellulose having a weight average molecular weight of 9,000 g / mol or less, and the second dispersant, which is polyvinyl butyral (PVB), is controlled to be 1:2.5 to 1:10, so that the initial viscosity and the rate of change of viscosity over time can be further reduced.

[0038] (1) Carbon nanotubes

[0039] The carbon nanotubes function as a conductive material in the dispersion of the present invention, and may be single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0040] There is no particular limitation on the carbon nanotubes used in the present invention, but preferably the carbon nanotubes have a diameter of 800 m 2 / g to 2,000m 2 / g specific surface area and 0.1 μm to 10 μm length. If the carbon nanotubes meet the above conditions, the conductivity can be particularly excellent. In addition, the specific surface area can be measured by the BET method, and more specifically, it can be calculated by the nitrogen adsorption at liquid nitrogen temperature (77K) using a specific surface area measuring device (BEL Japan Co., BELSORP-mini II). In addition, the above length can be measured using an atomic force microscope or a scanning electron microscope.

[0041] In the carbon nanotube dispersion of the present invention, the content of the carbon nanotube may be 5.0 wt% or less, and specifically, may be 0.1 wt% or more, 0.2 wt% or more, 0.3 wt% or more, 0.4 wt% or more, or 0.5 wt% or more, and 5.0 wt% or less, 4.5 wt% or less, 4.0 wt% or less, 3.5 wt% or less, 3.0 wt% or less, or 2.5 wt% or less. Meanwhile, if the content of the carbon nanotube is too low, when the carbon nanotube is used as a conductive material, etc., it is impossible to achieve sufficient conductivity, and if the content of the carbon nanotube is too high, the viscosity of the dispersion is excessively increased, so that the processability may be reduced.

[0042] (2) Dispersant

[0043] The carbon nanotube dispersion according to the present invention uses carboxyalkyl cellulose having a weight average molecular weight of 9,000 g / mol or less as a first dispersant and polyvinyl butyral (PVB) as a second dispersant in order to improve the dispersibility of the carbon nanotubes.

[0044] (2-1) First dispersant

[0045] The first dispersant used in the present invention is characterized by being a carboxyalkyl cellulose having a weight average molecular weight of 9,000 g / mol or less.

[0046] Specifically, the first dispersant may be carboxymethyl cellulose (CMC) or carboxyethyl cellulose (CEC). Cellulose-based components significantly contribute to suppressing the increase in viscosity of the dispersion over time and can improve the dispersibility of the carbon nanotube dispersion.

[0047] In the carbon nanotube dispersion of the present invention, the content of the first dispersant can be 0.1 wt % to 5 wt %, and specifically, can be 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 0.6 wt % or more, 0.7 wt % or more, 0.8 wt % or more, 0.9 wt %, or 1 wt % or more, and 5 wt % or less, 4.8 wt % or less, 4.6 wt % or less, 4.4 wt % or less, 4.2 wt % or less, 4.0 wt % or less, 3.8 wt % or less, 3.6 wt % or less, 3.4 wt % or less, 3.2 wt %, or 3.0 wt % or less.

[0048] If the content of the first dispersant component is less than the above range, the effect achieved by the carboxyalkyl cellulose is insufficient, so that the dispersibility of the dispersion may be reduced, or the change in the viscosity of the dispersion over time may increase. In addition, if the content of the first dispersant component is greater than the above range, when the carbon nanotube dispersion is applied to an electrode, the dispersant is excessive and the dispersant may act as an impurity in the electrode, thereby deteriorating the conductivity of the electrode.

[0049] Meanwhile, the weight average molecular weight (Mw) of the first dispersant used in the present invention may be 9,000 g / mol or less, preferably 2,000 g / mol to 8,000 g / mol, and more specifically 2,000 g / mol or more, 2,500 g / mol or more, 3,000 g / mol or more, 3,500 g / mol or more, 4,000 g / mol or more, 4,500 g / mol or more, or 5,000 g / mol or more, and 8,000 g / mol or less, or 7,500 g / mol or less.

[0050] (2-2) Second dispersant

[0051] The second dispersant used in the present invention is characterized by being polyvinyl butyral (PVB).

[0052] When applied to a carbon nanotube dispersion, the polyvinyl butyral dispersant of the present invention can prevent aggregation of carbon nanotubes through the interaction between butyral groups and carbon nanotubes, and as a result, the polyvinyl butyral dispersant can be particularly used to reduce the initial viscosity of the dispersion.

[0053] In the carbon nanotube dispersion of the present invention, the second dispersant may have a unit content of vinyl alcohol of 10 wt % to 22 wt % in polyvinyl butyral, and specifically, the unit content of vinyl alcohol may be 10 wt % or more, 11 wt % or more, 12 wt % or more, 13 wt % or more, 14 wt % or more, 15 wt %, 16 wt % or more, or 17 wt % or more, and 22 wt % or less, 21 wt % or less, 20 wt % or less, 19 wt % or less, or 18 wt % or less. If the unit content of vinyl alcohol is greater than 22 wt %, the interaction effect between the butyral group and the carbon nanotube may be reduced, so that the viscosity of the dispersion may increase.

[0054] In the carbon nanotube dispersion of the present invention, the content of the second dispersant can be 0.1 wt % to 5 wt %, and specifically, can be 0.1 wt % or more, 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 0.6 wt % or more, 0.7 wt % or more, 0.8 wt % or more, 0.9 wt %, or 1 wt % or more, and 5 wt % or less, 4.8 wt % or less, 4.6 wt % or less, 4.4 wt % or less, 4.2 wt % or less, 4.0 wt % or less, 3.8 wt % or less, 3.6 wt % or less, 3.4 wt % or less, 3.2 wt %, or 3.0 wt % or less.

[0055] If the content of the second dispersant component is less than the above range, the effect achieved by the polyvinyl butyral component is insufficient, so that the initial viscosity of the dispersion itself may increase excessively, and if the content of the second dispersant component is greater than the above range, the content of the cellulose-based component is relatively reduced, so that the change in viscosity of the dispersion over time may increase.

[0056] Meanwhile, the weight average molecular weight (Mw) of the second dispersant used in the present invention may be 20,000 g / mol or less.

[0057] The weight ratio between the first dispersant and the second dispersant may be 1:2.5 to 1:10, and specifically, based on 100 parts by weight of the first dispersant, the second dispersant may be 250 parts by weight or more or 300 parts by weight or more, and 1000 parts by weight or less, 900 parts by weight or less, 800 parts by weight or less, 700 parts by weight or less, 600 parts by weight or less, or 500 parts by weight or less. Within the above range, the synergistic effect between the first dispersant and the second dispersant is maximized, thereby allowing the carbon nanotubes to be uniformly dispersed in the carbon nanotube dispersion, so that not only the viscosity is low, but also the viscosity can be maintained at a constant level over time.

[0058] Meanwhile, the combined content of the first dispersant and the second dispersant may be 50 to 700 parts by weight, based on 100 parts by weight of the carbon nanotubes, and specifically, the combined content of the first dispersant and the second dispersant may be 50 parts by weight or more, 100 parts by weight or more, 150 parts by weight or more, or 200 parts by weight or more, and 700 parts by weight or less, 650 parts by weight or less, 600 parts by weight or less, or 550 parts by weight or less, based on 100 parts by weight of the carbon nanotubes.

[0059] If the combined content of the first dispersant and the second dispersant is greater than the above range, when the carbon nanotube dispersion is applied to an electrode, the conductivity of the electrode may be deteriorated due to the excessive amount of the dispersant and the dispersant may act as an impurity in the electrode. On the other hand, if the combined content is less than the above range, the effect of improving dispersibility, the effect of reducing viscosity, and the effect of suppressing the change in viscosity over time may be insufficient, and in particular, the stability of the viscosity may be significantly reduced due to the occurrence of gel shrinkage.

[0060] By controlling the weight ratio between the first dispersant and the second dispersant, the carbon nanotube dispersion of the present invention can reduce both the initial viscosity and the change in viscosity over time, and can achieve excellent coating processability and storage stability.

[0061] (3) Solvent

[0062] The solvent used in the present invention is a solvent for dispersing the carbon nanotubes and the dispersant, and when the carbon nanotubes in a powder state are used as they are in the preparation of the electrode slurry composition, the solvent may be used to prevent the aggregation of the carbon nanotubes.

[0063] As the solvent, a solvent capable of dissolving or dispersing the carbon nanotubes and the dispersant at a predetermined level or more may be used. The solvent may be included in an amount such that the electrode slurry composition has a suitable viscosity in consideration of processability of an electrode slurry composition to be prepared using the carbon nanotube dispersion.

[0064] The solvent is used to disperse the carbon nanotubes and the dispersant, and is not particularly limited as long as it is commonly used in the art, and may be, for example, one or more selected from the following: amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents, ester-based solvents, and aqueous solvents.

[0065] The amide-based polar organic solvent may be one or more selected from N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide, and dimethylacetamide (DMAc).

[0066] The alcohol-based solvent may be one or more selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol (or isopropanol), 1-butanol, 2-methyl-1-propanol, 2-butanol, 1-methyl-2-propanol, pentanol, hexanol, heptanol, octanol, glycerol, trimethylolpropane, pentaerythritol, and sorbitol.

[0067] The diol-based solvent may be one or more selected from ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexanediol.

[0068] The glycol ether-based solvent may be one or more selected from the group consisting of ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether.

[0069] The ketone-based solvent may be one or more selected from acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone.

[0070] The ester-based solvent may be one or more selected from ethyl acetate, γ-butyrolactone, and ε-propiolactone.

[0071] In addition, the aqueous solvent may be water.

[0072] When the initial viscosity is measured using a viscometer (viscometer TV-25, TOKI SANGYO Co.) at 25° C. and 1 rpm using rotor No. 1, the initial viscosity of the carbon nanotube dispersion of the present invention may be 10,500 cP or less, preferably 10,000 cP or less. In addition, while satisfying the above-mentioned initial viscosity conditions, the rate of change in viscosity of the dispersion per week may be 25% or less, preferably 20% or less.

[0073] The rate of change in viscosity per week is obtained by calculating how much the viscosity increases in one week when the dispersion is stored at 25° C. for one week, and can be calculated using the following Equation 1.

[0074] [Equation 1]

[0075] Viscosity change rate (%) = (viscosity after 1 week - initial viscosity) / (initial viscosity) * 100%

[0076] Meanwhile, the above viscosity can be measured using a viscometer (TV-25, TOKI SANGYO Co.) by starting measurement at 1 rpm using a No. 1 rotor and recording the value after 10 minutes.

[0077] Method for preparing carbon nanotube dispersion

[0078] The present invention provides a method for preparing the above-mentioned carbon nanotube dispersion, and specifically, provides a method for preparing the carbon nanotube dispersion, the method comprising (S10) mixing carbon nanotubes, a first dispersant, a second dispersant and a solvent, and (S20) dispersing the mixture.

[0079] In the method for preparing a carbon nanotube dispersion of the present invention, the carbon nanotubes, the first dispersant, the second dispersant, and the solvent are the same as described above.

[0080] Meanwhile, step S10 of mixing all the above components can be performed by a method generally applied to a mixing process, and for example, the step can be performed by setting an impeller and a container in a melt bath (Dispermat-CA, VMA-Getzmann Co.), followed by mixing at 400 rpm for 10 minutes, and then introducing carbon nanotubes therein and treating it at 8000 rpm for 60 minutes.

[0081] In addition, step S20 may be a step of dispersing the formed mixture to prepare a final dispersion. In this dispersing step, the physical properties of the carbon nanotubes in the dispersion may become uniform.

[0082] In addition, step S20 may include a step (S21) of stirring at a rate of 5,000 rpm to 10,000 rpm for 30 minutes or more, and preferably, may include a step of stirring at a rate of 8000 rpm for 60 minutes. By controlling the stirring rate and time as described above, a more uniform dispersion can be achieved, thereby keeping the viscosity of the obtained carbon nanotube dispersion low.

[0083] The initial viscosity of the carbon nanotube dispersion prepared by the method for preparing a carbon nanotube dispersion of the present invention can be 12,000 cP or less, preferably 10,000 cP or less. In addition, while satisfying the above-mentioned initial viscosity conditions, the weekly viscosity change rate of the dispersion can be 30% or less, preferably 20% or less.

[0084] Hereinafter, the present invention will be described in more detail with reference to embodiments and experimental examples, but the present invention is not limited by these embodiments and experimental examples. Embodiments according to the present invention can be modified into other various forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

[0085] Material

[0086] Prepared with 1,160m 2 Carbon nanotubes (TUBALL, OCSiAlCo.) having a specific surface area of ​​100 μm / g and a length of 5 μm or more were prepared. N-methyl-2-pyrrolidone (NMP) was prepared as a solvent.

[0087] As the first dispersant of the embodiment, carboxymethyl cellulose (weight average molecular weight 5,200 g / mol) or carboxyethyl cellulose (weight average molecular weight 7,000 g / mol) is used, and as the second dispersant of the embodiment, polyvinyl butyral (product name: Mowital B14S, Kuraray Co. / weight average molecular weight: 10,000 g / mol, polyvinyl alcohol content: 14 wt % to 18 wt %) is used.

[0088] As the first dispersant of the comparative example, methyl cellulose (weight average molecular weight: 9,000 g / mol), carboxymethyl cellulose (weight average molecular weight: 250,000 g / mol), carboxymethyl cellulose (weight average molecular weight: 5,200 g / mol), or poly(9-vinyl carbazole) (product name: poly(9-vinyl carbazole), Sigma-Aldrich Co.) was used, and as the second dispersant of the comparative example, phenol novolac (product name: KPH-F2002, Kolon Industries Co.), hydrogenated nitrile rubber (HNBR) (product name: Therban AT 3404, Arlanxeo Co.), or polyvinyl butyral (product name: Mowital B14S, Kuraray Co. / weight average molecular weight: 10,000 g / mol, polyvinyl alcohol content: 14 wt % to 18 wt %) was used.

[0089] Examples and Comparative Examples

[0090] The first dispersant and the second dispersant of the above materials and NMP as a solvent are mixed to prepare a mixture. The impeller and the container are set in a melt bath (Dispermat-CA, VMA-Getzmann Co.), and then the dispersant and the solvent of the mixture are mixed by stirring at 400 rpm for 10 minutes. Carbon nanotubes (TUBALL, OCSiAl Co.) are introduced thereinto so that the content thereof in the dispersion is 0.6% by weight, and treated at 8,000 rpm for 60 minutes.

[0091] The resulting product was treated 10 times using a high pressure disperser (PICOMAX, Micronox Co.) at a pressure of 20,000 psi to prepare a carbon nanotube dispersion.

[0092] The concentration of the carbon nanotubes used in each of Examples and Comparative Examples, the type and content (based on the total dispersion weight) used therein, and the weight ratio between dispersants are summarized in Table 1 below.

[0093] [Table 1]

[0094]

[0095] Experimental Example: Determination of initial viscosity of dispersion and rate of change of viscosity

[0096] The viscosity was measured for each of the carbon nanotube dispersions of Examples 1 to 4 and Comparative Examples 1 to 9, and the viscosity was measured again after the carbon nanotube dispersions were allowed to stand at 25° C. for 1 week, and the results are shown in Table 2 below.

[0097] The viscosity was measured using a viscometer (TV-25, TOKI SANGYO Co.) at 25° C. and 1 rpm using a No. 1 rotor.

[0098] [Table 2]

[0099]

[0100] As can be determined in Table 2 above, when Examples 1 to 4 and Comparative Examples 1 to 9, in which the same carbon nanotubes and the same solvent were applied at the same content, were compared, it was determined that Examples 1 to 4, in which the first dispersant and the second dispersant of the present invention were used in a specific weight ratio range, had low initial viscosities and also had low viscosity change rates after one week. On the other hand, it was determined that in the case of Comparative Example 1, in which the first dispersant of the present invention was used alone, the change rate of viscosity was low, but the initial viscosity was as high as 13,000 cP, and in the case of Comparative Example 2, in which polyvinyl butyral (PVB) was used alone, the initial viscosity was low, but the change rate of viscosity was as high as 34%.

[0101] In particular, it has been determined that in the case of Comparative Examples 3 and 4 in which hydrogenated nitrile rubber (HNBR) or phenol novolac was used as the second dispersant, the initial viscosity and the rate of change in viscosity were too high, or the initial viscosity was too high to measure the viscosity, so that the storage stability and workability were significantly reduced.

[0102] Similarly, in the case of Comparative Example 7 in which poly(9-vinylcarbazole) (a component different from the first dispersant of the present invention) was used as the first dispersant, or in the case of Comparative Example 8 in which methyl cellulose was used instead of a cellulose-based component or carboxyalkyl cellulose, and in the case of Comparative Example 9 in which carboxyalkyl cellulose having a weight average molecular weight much higher than that required in the present invention was used, there was a problem that the initial viscosity and the rate of change in viscosity were too high, or the viscosity measurement itself was difficult as in the case of Comparative Examples 3 and 4.

[0103] Finally, in the case of Comparative Examples 5 and 6 in which both the first dispersant and the second dispersant were used but the ratio therebetween was inappropriate, the viscosity change rate was 30% or more (which was too high), or the initial viscosity was 12,500 cP (which was too high).

[0104] From the results, it has been confirmed that the dispersion of the present invention has excellent processability due to low initial viscosity and low viscosity change rate, and accordingly, has improved storage stability.

Claims

1. A carbon nanotube dispersion comprising: Carbon nanotubes; a first dispersant; a second dispersant; and Solvents, in: The first dispersant is a carboxyalkyl cellulose having a weight average molecular weight of 9,000 g / mol or less; The second dispersant is polyvinyl butyral (PVB); and The weight ratio between the first dispersant and the second dispersant is 1:2.5 to 1:

10. 2 . The carbon nanotube dispersion according to claim 1 , wherein a combined content of the first dispersant and the second dispersant is 50 to 700 parts by weight based on 100 parts by weight of the carbon nanotubes. 3 . The carbon nanotube dispersion according to claim 1 , wherein the first dispersant is present in an amount of 0.1 wt % to 5 wt % based on the total weight of the dispersion. 4 . The carbon nanotube dispersion according to claim 1 , wherein the second dispersant is present in an amount of 0.1 wt % to 5 wt % based on the total weight of the dispersion. 5 . The carbon nanotube dispersion according to claim 1 , wherein the carbon nanotube content is 5 wt % or less based on the total dispersion weight. The carbon nanotube dispersion according to claim 1 , wherein the first dispersant is carboxymethyl cellulose (CMC) or carboxyethyl cellulose (CEC). 7 . The carbon nanotube dispersion of claim 1 , wherein the first dispersant has an average molecular weight of 2,000 to 8,000 g / mol. 8 . The carbon nanotube dispersion according to claim 1 , wherein the second dispersant has a unit content of vinyl alcohol of 10 to 22 wt % in the polyvinyl butyral. 9 . The carbon nanotube dispersion according to claim 1 , wherein the second dispersant has an average molecular weight of 20,000 g / mol or less.

10. A method for preparing the carbon nanotube dispersion according to claim 1, the method comprising: (S10) mixing carbon nanotubes, a first dispersant, a second dispersant, and a solvent; as well as (S20) The mixture is dispersed. 11 . The method according to claim 10 , wherein the above step S20 comprises ( S21 ) stirring at a rate of 5,000 rpm to 10,000 rpm for 30 minutes or more.

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